Liquid level indicator

Home brew electronics for home brew beer -- it's s.e.b. synergy!

Mr. Popelish's suggestion is a great choice. But you might want to reconsider the float concept. Many small floats are made for food service (i.e. they can be washed down, scrubbed and sterilized), and the built-in hysteresis of a magnetic float can make this the easiest solution. If you can't do that for one reason or another, you still have a number of options, besides the capacitive sensor. They''re all going to be more expensive and more difficult, though.

By placing the vat on a scale or load cells, you can weigh the vat and its contents. But if you're going to use the information for anything, you need some kind of output from the scale. You can get one with serial communication output and interface to a PC. Scales are also made with analog outputs, which might allow you to do this without a PC. In fact, many of the simplest scales have an analog front end feeding either an A-to-D converter with LED/LCD display, or a uC analog input. If you're crafty, you might be able to pick that off and use it for your control circuit. Downside, of course, is that you have to be careful about movement (kind of hard if you've got an agitator). Also, any motor or other equipment may have to be weighed along with the vat.

Some ultrasonic sensors are made for this and have discrimination circuitry built in which can ignore the foam and output the result from the strongest signal rather than the first. However, these are fairly expensive, especially for a home brew setup. You would also have to have the sensor face inside the tank, and cleaning/sterilization limits your choices.

If you can live with something which goes through the wall, but is fairly flush and also has food service rating, you might want to try some of the retroreflective sensors made by Gems and other manufacturers. They send out a light beam to a prism which extends into the vat. Air and foam on the face of the prism will force almost all of the light to reflect off the prism and back to the sensor. When the beer comes in contact with the prism, though, most of the light just goes straight through the glass into the liquid. Less expensive than the ultrasonics, but you still have to pierce the vat. In addition, there's no hysteresis, which may mean you'll have to install two sensors.

If your vat is white Nalgene or another translucent material, you might be able to get away with using a couple of photoresistors to sense light through the vat itself. This might be a bit of a touchy adjustment, though, and might be very dependent on ambient light.

There are several other much more expensive methods to level sense beer or other foaming liquid, but I would guess they're beyond your budget.

The float is the least expensive and most efficient solution. If I were in your shoes, I would get a Gems catalog or check out their website and take a good look at what they have for food service floats. IMHO, that would be your best bet if you're on a budget. And by the way, they have live phone help from 8 to 4:30 EST M-F. If you're in a hurry, just call them up and ask for help. They don't mind onesie applications. You can get much of their product line sent direct from Newark and have your solution tomorrow.

Good luck Chris

You might Google "capacitive proximity". These are devices that switch an output signal when conductive material gets close to their face. Some can operate through glass or plastic container walls.

--- I'd use a self-heated thermistor.

Since the heat capacity of beer is greater than that of air, when the beer hits the thermistor it will suck heat out of it, causing its temperature to fall, causing its resistance to rise. You can buy thermistors in threaded mounts from Omega Engineering (pricey) which will screw right into the container, and then with a couple of resistors, a pot, a comparator, and an LED, you can put together a circuit to do exactly what you want. Would you like a schematic?

-- John Fields Professional Circuit Designer

Mark. Check out the "motor home" dealers. They use something to detect water level in potable water tanks. W W

You cold attach some aquarium tubing to the bottom of the container so the beer could flow in. Run the tubing up wards and attach to a micro switch above the top of the container. At the level where you want to activate the micro switch to run the pump, make horozontal coils of the tubing so it will get heavier as the coils fill and pull down on the micro switch to activate the pump. There are other setups, but I like this one.

Get one of those "touch to on" lamps.

Take two insulated copper wires, say 18 SWG and attach them to your vessel in such a way that when your liquid reaches the desired level, the two copper wires touch the liquid.

Connect the other end of one of the copper wire to earth Connect the other end of the second copper wire to the touch lamp's body

Connect your pump to the AC output of the touch lamp (where you're supposed to fix a light bulb)

Connect a relay to the AC output of the touch lamp, in such a manner that when energised, it shorts the lamp's body to earth.

Mike

I meant connect energizing coil of relay to AC output of touch lamp.. (of course the relay should have an AC mains driven coil)..

This is to clamp the pump on (even after the liquid level goes down or there are waves in the vessel).

Mike

---------------- Automatic washing machine's depth sensor. Works with a pressure switch up top and a clear vinyl tube down into the basin. Any appliance supply store. Adjust by moving the tube up and down.

-Steve

--
-Steve Walz  rstevew@armory.com   ftp://ftp.armory.com/pub/user/rstevew
Electronics Site!! 1000\'s of Files and Dirs!!  With Schematics Galore!!
http://www.armory.com/~rstevew or http://www.armory.com/~rstevew/Public

Thanks for all the suggestions everybody.

I'll explore each of them individually.

I spotted these in RS #354-290. The seems to be quite a pro sort of thing. They have a relay control unit, but I need to add a few of my own other features, to I'd have to interface to them myself. I'm not sure how to create an alternating voltage (flip-flop?), and evern more so, I don't know how to measure the resistance via AC voltage/current.

Cheers, Mark

Somebody on my brewing forum suggests this cct, which seems good.

I am abit of a newbie, can anybody explain to me what's going on here?

on another probe, which is then rectified and 'compared' to a reference level which energises the relay. Which bits of the cct do what parts/how they do it, I'm not sure about.

I need to be able to alter this circuit by taking the logical state(0 or 1) of the sensor output, and combining it with a few other gates before then driving the output relay.

I'm always bad at understanding transistors, and CMOS outputs. Why does he use PNP rather than NPN here? Does it matter? Can I use say BC107's (which I have at home) instead?

Regards, Mark

Hi, Mark. Tony Van Roon's circuit uses 2/4ths of a 4093, which is a quad 2-input NAND gate with Schmitt trigger. The gate shown as N1 is set up as a cheapie oscillator, and outputs a square wave (0V - 12V) at a frequency of a couple of KHz. This signal is AC coupled through the caps C1, C2 and the liquid (which is assumed to have a relatively low resistance) to the second part of the circuit. It's then half-wave rectified and level-shifted by diodes D2 and D3 so as to charge up capacitor C4. If the cap goes up to more than 60% or so of the power supply (that would be around 7.5 to 8V in the diagram), that will send N2 low. According to the diagram that will turn on the transistor T1, which will turn on the relay.

First off, there's a conceptual problem here, which you'd find out as soon as you tried to use this thing. I'm assuming your beer vat is going to have foam. If the liquid is conductive (I believe beer is), then the foam will be, too. Your basic idea, I believe, was sensing fluid level, not foam level. Also, foam sticking on the electrodes may cause the resistive path to remain unless you have them far enough apart. Something to think about, but depending on the electrodes you use and their spacing, it might be OK.

Second, the circuit shown is somewhat deficient in a couple of areas. A transistor is a current-driven device. When you try to drive the base of a transistor with a voltage, the bulk resistance of the transistor plus the output impedance of the logic gate _may_ be enough to save the transistor, but you should never depend on it. While you're at it, you should know that the relay load really should be connected to the collector rather than the emitter. Second, resetting the logic gate by opening up the GND connection is an invitation for all sorts of bad things to happen, as the cap tries to discharge through other pins of the IC.

Here's another try that avoids these problems (view in fixed font or Notepad):

` VCC VCC ` + + ` | | ` | C| ` Sensor 1N4002 - C|RY1 ` ^ C| ` ^ ^ | | ` | | | | ` C| C| '----o ` --- --- | ` --- --- __ __ | ` ___ | | .--| | .--| | ___ |/ ` .-----|___|--o o->|-o---o---o---| |&H|o-| |&H|o-|___|-o-| Q ` | | | C| | | '--|__| '--|__| R | |>

` | __ | - --- .-. .-. .-. | ` | .--| | | ^ --- | | | | R| | | ` o--| |&H|o--o | | | | | | | | | ` | '--|__| | | '-' '-' '-' | ` | === === | |22 ohm | | ` C| GND GND === | === === ` --- GND o | GND GND ` --- |=| ` | o | ` === |Reset ` GND | ` === ` GND created by Andy´s ASCII-Circuit v1.24.140803 Beta

Everything above is the same as Tony's circuit, except as shown. The cheesy reset was replaced with a 22 ohm resistor in series with a switch to discharge the cap. That should take care of resetting the relay circuit if you need it. Second, Tony's circuit has an active low logic output driving a PNP transistor. By using one of the spare inverters, you've got an active high signal which drives an NPN. The last change is that you've got the relay load at the collector of the transistor, and there's a series resistor R to the base of the transistor along with a base ballasting resistor to make sure it's really off.

You haven't mentioned what relay you're using, but I'll assume it's one with a coil power of about 3/4 watt. For a 12V coil, that would mean about 60 mA. It's customary, when using a small signal transistor as a switch, to drive the base with a current of about 1/10th of the collector current. If you set R so that the 4093 output is pushing

6mA, you'll be in the Groan Zone. That's too much current to pull from a regular 4000-series CMOS output at 12V. But, it should be OK for two CMOS outputs. So, you might want to try replacing the third gate with this (view in fixed font or Notepad):

` ` VCC VCC ` + + ` | | ` 1N4002| C| ` - C|RY1 ` ^ C| ` | | ` __ | | ` .--| | ___ '----o ` | |& |o-|___|--. | ` o--|__| 3.9K | | ` | | |/ `---o o---o-| Q ` | | | |>

` | __ | .-. | ` o--| | ___ | | | | ` | |& |o-|___|--' | | | ` '--|__| 3.9K '-' | ` 10K| | ` === === ` GND GND ` ` created by Andy´s ASCII-Circuit v1.24.140803 Beta

This way, you've also finished all the 4093 gates on your IC, and found a good use for each of them.

Good luck, and feel free to ask if you have any further questions. Chris

Hi Chris

Thanks very much for taking the time to explain this for me, and offer improvements.

I've printed off your message and ccts from notepad for a thorough read.

If you can suggest a good electronics book which explains transisters very well for beginners/noddy's, that would be great.

You may be right about the foam, but I'm hoping to build the U/back and hop back in such a way that I get minimal foaming - hopefully I can achieve this.??

For my cct, I need to drive the relay from two sensors - a high and low water mark, and I'd like to provide both a reset and an override ("just turn the pump on") feature. Furthermore, I'd like to be able to use the same cct and switch between the underback sensors and the hop back sensors (DPDT switch?). It may be that I'll need two separate sensor ccts for this, as each may need to be calibrated separately. Dunno.

Any suggestions you have here would be very welcome! I did draw up a truth table for the kind of logic I think I need, here

(go to the bottom of the page for the table).

This means that I need an assortment of AND, OR and INVERTER gates. I know each of these can be built from NAND gates (IIRC OR gate made from

3 NAND's), but this is a bit messy. Any suggested improvements here would be very welcome too!

I forgot to include schmitt triggers on some of the switched inputs, so I guess a schmitt NAND like the cct above or a dedicated schmitt trigger is in order here?

Cheers, Mark

Oh, btw Chris, the relay I was planning on using was model YX97F from Maplin electronics. Technical info for this is very thin on the ground indeed, but IIRC, the coil has an impedence of about 330 ohms.

I calculate this to mean 36mA through collector of transistor, and using your 10th rule for base current, this gives 3.6mA.

Would this mean I can just use a single NPN (I have BC107B's at home) or is this still too much for the poor blighter? (sorry, I don't have the spec sheets in front of me to check, but it still sounds high for a signal transistor).

Perhaps a Darlington pair would be better for driving the relay here?

Cheers, Mark

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Hi, Mark. Sorry about the delay in response. Busy with other things over the weekend.

Your project looks like it's well though out, with a lot of time and sufficient money having been invested. Boy, you're serious about beer. Good job.

Your truth table seems to describe the function of a drain pump. Turn on when H and L are ON, and don't turn off until H and L are OFF. This action is described as a SET-RESET (SR) latch, which is a type of flip-flop (FF). Again, you can see how using one of the Gems floats with hysteresis would make things much simpler here. Many of their sensors can be set so the microswitch or hall effect switch will not go on until the float reaches a higher position, and then will stay on until the float reaches the lower position. This hysteresis would simplify things quite a bit. And I would personally really recommend you use something that's made for the application. If you asked me to do the electronics for this, I'd select a Gems switch (actually two -- you'll want one for overflow check, too), and see if I could do what you needed with the float switch contacts and another switch or two. But there it is. Let's see what we can do with logic gates, transistors and relays.

Before anything else, you should know your transistor should be OK for switching a 12VDC 36mA relay coil. Your BC107B is a small signal amplifier transistor with a Vceo of 50V (how high a voltage it can handle), an Ic(max) of 100mA (maximum collector current) and a minimum Hfe (DC current gain) of 200. This is good news, because the "rule of

10" actually says that if you're switching a given collector current load, you should inject 10X the current suggested by the DC current gain. Or, if you like, the equation:

Ib =3D Ic / (Hfe /10)

That would mean you need a base current of 36 mA / (200 / 10) =3D 1.8 mA. That's good news because a 4000-series CMOS gate won't have a problem sourcing or sinking 1.8 mA with a power supply of 12VDC.

Now let's take a look at the circuit requirements. You've gone beyond what you can do with a "one chip solution", unless you were to use a PIC or BASIC Stamp. So let's splurge and use a 555 for your oscillator signal (you're going to need those gates for other things).

`Beer Oscillator ` ` VCC VCC VCC ` + + + Osc Out ` | | | ^ ` .-. .---o-----o---. | ` | |68K | 8 4 | | ` | | | | --- ` '-' | | --- ` | | | | ` o-------o7 | | ` | | 3o---------' ` .-. | | ` | |10K | 555 | ` | | .---o6 | ` '-' | | | ` | | | | ` o---o---o2 | ` | | | ` --- | | ` --- | 1 5 | ` |.01uF '---o-----o---' ` | | ` =3D=3D=3D =3D=3D=3D ` GND GND ` created by Andy=B4s ASCII-Circuit v1.24.140803 Beta

This oscillator should be good for driving almost an infinite number of your 4093 sensors at somewhere near the same frequency as your 4093 oscillator. Just remember that you have to keep both the oscillator signal and the sensors disconnected from earth ground or any other potential. This is called a "floating" signal. ;-)

Let's review the bidding on these sensors. Now, both the high and the low stainless probes are going to have one of these on the receiving side like you talked about before:

` Beer Sensor ` H (or L) Probe` ` ` ^ ` | ` --- ` --- __ ` C | .---| | ` o---->|-o----o--o |&H|o---> H (or L) ` | D | | '---|__| ` - --- .-. 1/4 4093 ` D ^ --- | | ` | C| | |15 Meg ` | | '-' ` | | | ` =3D=3D=3D =3D=3D=3D =3D=3D=3D ` GND GND GND created by Andy=B4s ASCII-Circuit v1.24.140803 Beta

OK. Now, we have two 12V logic signals that go active low when they sense liquid level. We're getting there. Let's be creative and call these signals H and L.

Time for a little diversion here. Look at this little trick:

` The Dreaded NOR RS Flip Flop ` __ ` R o-------|>=3D| .-------------------. ` |1 |o-o----o Q | S | R | Q | Q' | ` .----|__| | | | | | | ` | | | 0 | 0 | No Change | ` | | | | | | | ` | .--------' | 0 | 1 | 0 | 1 | ` | | | | | | | ` '----------. | 1 | 0 | 1 | 0 | ` | __ | | | | | | ` '--|>=3D| | | 1 | 1 | 0 | 0 | (disallowed) ` |1 |o-o----o Q' | | | | | ` S o--------|__| '-------------------' `created by Andy=B4s ASCII-Circuit v1.24.140803 Beta

You can hook up a couple of NOR gates (CD4001) and feed their outputs back into their inputs to do this trick. We can use this to get your flip flop action, because you want the RS FF to SET when H is low and L is low, and you want the RS FF to RESET when H is high and L is high. Here's how:

` Beer Flip Flop VCCVCC ` + + ` | | ` __ - C| ` .--| | ^ C| ` H >--o-o |& |o--. | C| ` | '--|__| | | | ` | | '--o ` | | __ | ` | '---|>=3D| "R" __ | ` | |1o|o-----|>=3D| ___ |/ ` | .---|__| |1 |o-o--|___|- -| BC107B ` | | .----|__| | 6.8K | |>

` | | | | .-. | ` | | | | | | | ` | | | .--------' 10K| | | ` | | | | '-' | ` | | '----------. | | ` | | | __ | =3D=3D=3D =3D=3D=3D ` | | __ '--|>=3D| | GND GND ` '-----------|---|>=3D| |1 |o-o ` | |1 |o-----|__| ` .-----------|---|__| "S" ` | __ | ` | .--| | | ` L >--o-o |& |o--' ` '--|__| `created by Andy=B4s ASCII-Circuit v1.24.140803 Beta

You can see from the diagram that the "S" input only goes high when H and L are low, and the "R" input to the FF only goes high when H and L are high. (Note: logic ICs have power connections which were not included here. Pin 14 is +12V and pin 7 is GND for both the 4001 and

4093.)

You can get your Override/Reset action by putting a switch in with the relay above like this:

` VCC VCC ` + + ` | | ` | | ` - C| ` ^ C| ` | C| ` | | Override ` | | _/ ` '----o---o/ o--. ` | | ` | | ` | | ` |/ | ` >-| | ` |> | ` | | ` | | ` =3D=3D=3D =3D=3D=3D ` GND GND created by Andy=B4s ASCII-Circuit v1.24.140803 Beta

There's a lot more you can do with this stuff, but it's a little tedious in ASCII art. This should give you a start. Feel free to email me if you have any questions. And you might want to wait a day or so before building -- there are several really good electronics people in this ng who may spot an error in the above or have a better idea.

By the way, also feel free to let us know how you're doing.

Good luck Chris

Hi Chris

Yes, I do seem to take beer very seriously! The quality of it at least!

Thanks very much for such a detailed response. I really appreciate you taking the time to explain this stuff to me. All that you say makes sense.

I may have missed this, but I assume I need to have a 'common' probe, and then the H & L probes?

Hey, the ovverride switch is very neat - so simple, why didn't I think of that! :) - got carried away with the logic gates I guess! No need for a resistor here at all?

I actually need to control/pump/empty two seperate vessels (not at once

- they share the pump). How would you suggest I switch between one set of sensors and another? Two identical circuits, but switch the final pump drive from an OR gate or switch between one cct or another in to the relay coil?

btw, I did look at the commercial float switches and considered them a bit pricey (maybe you have a good diy source?). Not sure what's involved with using these things - are they just simple switches?

It's not likely I'll get to build the cct in the next few days anyway - work is rather busy at the moment - working weekends etc. :(

Thanks again Cheers, Mark

Yes, Mark, you will actually need three electrical connections for each tank -- H, L, and common. The current flows through the OSC. output into the H and L inputs, charging up the caps to change the logic state. If you've got a metal tank or have a metal drain, it may be easier to attach the oscillator output to that rather than have a third probe for each tank.

The bypass/override switch acts in the exact same way as the transistor switch in parallel with it -- they both provide a very low impedance path to GND when ON. It won't hurt the transistor at all to wire a switch in parallel with it, because of the protection diode across the relay coil. The inductive kick caused by the relay turning off will be recirculated by the diode, whether the switch or transistor turned off.

If you had two pumps as well as two vessels, you might want to just use a 4P3T switch to transfer control from one to another. But you only have one pump for two vessels. If the one you're not using is always empty, you can just run the two sets of sensors in parallel (H or L will go active if either one of the sensors is making continuity). But if you're using both vats at once, make the oscillator common go to both vats, and just use a DPDT switch to switch between H and L sensor inputs. This is very low frequency stuff (2KHz signal) so you don't have to worry about frequency effects at all.

` ` Vat 1 ` ` .---------------o-------> Upper Probe ` | ` o---' ` H o----o--__ .------------o-------> Lower Probe ` o------|---. ` | | ` | | .----o-------> Common ` | | | ` | | | ` o------' | | ` L o----o--__ | | ` o------. | | ` | | | Vat 2 ` | | | ` | '---|----o-------> Upper Probe ` | | ` Osc o--------. | | ` | '-------|----o-------> Lower Probe ` | | ` | | ` '--------------o----o-------> Common ` created by Andy´s ASCII-Circuit v1.24.140803 Beta

If you go with this, you may want to figure out some way to ensure that the pump valve and the switch are going in the right direction. Either that or you can rely on your Bavarian sense of Teutonic thoroughness to make sure every time. ;-)

Float switches are a bit pricey. But "in for a penny, in for a pound". When I contract test or automation jobs, I try to reach an accomodation with the customer. The goal, as always, is to provide the right balance between function, reliability and total customer cost. It's the customer's business, money and goals, so the decision about how to proceed and what to spend is always the customer's decision.

Looking at the great job you've done on the rest of the project, and the obvious investment in money, time, and intelligence, I would assume the most reliable solution would be more important to the customer than lowest cost. I believe that would be float level sensors, even though they're more expensive. But this resistive probe option seems like fun, and if you construct it well, it should be reliable (especially if you have an external safety in case of electronics failure). This is a hobby, and it's about the journey as well as the destination, right? I think this modification to the circuit you found on the net is fairly straightforward, and should work well if constructed properly.

Be sure to put the electronics in an enclosure which will resist splashing. Take the time to label everything, especially connectors and switches. Also, make sure you document your circuit and keep the documentation with your equipment. You'll be able to get help if you've got a problem then, and you won't have to remember what you did several months or years later if there's a glitch.

Good luck and Cheers, Chris

Hi Chris

I'm planning on using some small stainless steel vessels for the 'tanks' - only about 1-2 litres capacity required for each. The Will have a metal drain, so I'll try to find a way of attaching the OSC to this.

I was thinking about using two switches - one for manual/automatic and another for on/off for the pump in manual mode. I assume I can just interject these in to the collector of the relay driver transistor? I assume switch noise isn't an issue when energising the relay?

With regards to the re-use of the pump: The brewery setup is going to have quite a few plumbing valves, so these will be set to the required settings before firing up the electronics. Of course, with so many valves to worry about (see

I am a bit concerned that I'll get them wrong sometimes, so what I plan to do is print off a couple of lookup sheets and laminate them to keep them nice and dry, which tells me what setting each valve should be in for each stage of my process. Brewing is a fairly timeconsuming and slow-moving process, so it shoouldn't be difficult to make sure everything is setup ok, especially with a checklist. It's when things start going wrong that it gets a bit lively!

Re "in for a penny" - given no wife/family, I'd agree, but I've spent "most of the budget" on the actual brewing equipment, so the luxury stuff (like this control stuff), needs to be done on a budget, but hey it's fun to do this stuff, and it's much more to talk about and show off to your friends!

If I find I have problems with the sensors 'sensing' foam and such like, then I'll have to re-think (the time delay will help with spending more, I'm sure! :) )

Actually, I'll be needing to update this hardware to include a heater in one of the vessels (the underback). I was thinking I could use a temperature controller (FE33L - Maplin, has LCD display etc - cool), but I only want the heater to come on when the temp controller says "too cool" (fine, theres a signal from FE33L for this @1.5v), *AND* when the pump is on. This part I'm not 100% sure about, because the auto/manual + on/off switching complicates things a bit.

Any suggestion on how to do this? (obviously another relay+transistor etc) I assume some kind of AND gate with pump signal and temp ctrl?

Cheers, Mark

I seem to remember that there are optical level sensors that work for liquids that are not transparent. They give an electrical signal as an output which you can trigger on.

Fred.

Hi, Mark. Apart from just turning off the power, you can use a 3-way SPDT switch (ON-OFF-ON) to give you both the pump OFF and pump OVERRIDE functions like this:

` ` VCCVCC ` + + ` | | ` - C| ` ^ C| ` | C| ` | | ` '--o ` | ` Logic | Override ` o | o ` | | ` ___ |/ Pump | ` -|___|-o-| Off =3D=3D=3D ` | |> GND ` .-. | ` | | | ` | | =3D=3D=3D ` '-' GND ` | ` | ` =3D=3D=3D ` GND ` created by Andy=B4s ASCII-Circuit v1.24.140803 Beta

The switch actually has three positions -- up, middle, and down. In the middle position the switch pole isn't connected to either throw. That makes it an ideal, relatively easy hardware solution.

When you have any kind of low voltage high input impedance sequential logic, static from machine operators and moving parts and electrical noise can be a PITA, changing logic states and damaging ICs. Actually, as the prices of PLCs (Programmable Logic Controllers) came down to reality in the early 1990s, I basically stopped doing any factory industrial control circuits with 4000-series CMOS just for that reason. PLCs generally have optoisolated inputs and RC filters on the inputs to reduce the chance of electrical noise or ESD getting through. And again, this is another good reason for using a float. It's not affected by any of this stuff. But there are ways to deal with EMI/RFI in CMOS circuits...

First, you obviously wouldn't have any chance at all if the FF inputs were just hanging out in the breeze. But the caps and the schmitt trigger inputs condition the "real world" inputs and will effectively prevent electrical noise from affecting them (assuming you're using good caps and your circuit layout has a good low impedance ground path). Noise might affect the FF itself, though.

In order to minimize the risk of that occurring, you can do several things. The first and most important thing is to try to prevent the inductive kick of the pump switching off from creating a big spark that will cause EMI. To do that, you should place a snubber across the load. For AC loads (you are using an AC pump, right?), you should use an R-C snubber across the load.

` ` || ` .-------||----o------o------. ` | || | | | ` | RY | | .-. | ` | .-./ R| | |Pump `240VAC _ | / | | C| ` / \\ MOV |/| '-' C| ` ( ~ ) / | | C| ` \\_/ /'-' C | | ` | | | --- | ` | | --- | ` | | | | ` '-------------o------o------' ` created by Andy=B4s ASCII-Circuit v1.24.140803 Beta

You want to choose an R based on the maximum switching current of your relay. Let's say you've got 240VAC, a 5 amp relay contact, and a 1/2 amp pump. You then want a value for R which will bring the current fairly close to the rated current. If you use 100 ohms, that will get you to about 3 A switching current. You can then choose a value for C (line-rated cap, of course) which will just keep the relay contacts from arcing. For relays with clear cases, you can actually watch the arc disappear as you increase the value of C. For enclosed relays, you should remove the cover to check. You didn't mention pump current, but I'll guess it's rated for less than half an amp. For that sized pump, I would start with 0.1uF and see what happens. Among my trove of delightful stuff I've got a small box of different sized Quencharcs to just plug in and see what works. But it seems ITW/Paktron is having difficulty with getting distributors for their product these days, so you'll have to use discrete parts. Try the Cornell-Dubilier MMP6P1K (0.1uF, 600V, self-healing polyester film, you can get this from Farnell if you reference Newark P/N 95F7892) and a 100 ohm 1 watt or greater resistor.

Unless you've got a particularly large pump, this should do the job. To make it just about the perfect snubber, put a 280VAC rated MOV across the R-C snubber (the bigger the better - physical size on MOVs is proportional to joule rating). That will prevent the voltage across the cap from exceeding the rated voltage on the inductive kick, which will basically mean the snubber will last forever. It's preferrable to put the snubber/MOV across the load, but if that's not practical, you can put it across the relay contacts.

Having reduced or eliminated the relay spark, it's still better to put the relay physically as far away from the logic circuit as practical. The worst thing you can do is use a PC mount relay, and put the relay right next to the FF IC (don't laugh -- I did it once long ago). To quote from the wisdom of '70s vintage Sesame Street, "The Solution... To Pollution... Is Dilution". If you've got a source of EMI/RFI pollution, the farther away it is, the lesser effect, the better. It might even help to mount the relays for the control logic in another enclosure next to the pump, and have low voltage control lines going from the controller box to the relay box.

On the IC side, there's a few things you can do. Bypass the Vcc pin of each IC with an 0.1uF ceramic cap to GND. Keep the wires of the FF as short as possible, by using two NORs on one side of the IC and using direct wiring there.

Between working on the relay (EMI source) and the IC (EMI target), you should be in pretty good shape. Experiment around a little here once you've constructed this. Try switching two pumps if you have them, and see if this affects things. If you don't have two pumps, try putting a greater load on the pump (momentarily lock the rotor or put a friction load on) and see if the increased noise causes the logic circuit to upset. This isn't a proof that your solution works, but it helps to give confidence in the work you've done. The fact is, a hobbyist doesn't have the tools to really solve this kind of problem, so the best you can do is build up a lot of protection, test it as best you can under real world conditions, and then hope for the best. But with only one FF on one IC with no inputs extending from the immediate area, you shouldn't have much to worry about after you do the above stuff.

Your little controller board (amazingly, only 10 pounds!) seems to have a logic level output for heating. Again, you can use relay logic to make sure the heater is on only when the pump is on like this:

` ` || || ` .-------||----o------o------o------||------. ` | || | | | || | ` | CRY1 | | .-. | CRY2 | ` | .-./ R| | |Pump | `240VAC _ | / | | C| .-. ` / \\ MOV |/| '-' C| Heater| | ` ( ~ ) / | | C| | | ` \\_/ /'-' C | | '-' ` | | | --- | | ` | | --- | | ` | | | | | ` '-------------o------o------o--------------' ` ` ` VCC VCC ` + + ` | | ` - C| ` ^ C| RY2 ` | C| ` | | ` '---o ` | ` LO from ___ |/ ` FE33L >-|___|-o-| ` | |>

` .-. | ` | | | ` | | =3D=3D=3D ` '-' GND ` | ` =3D=3D=3D ` GND created by Andy=B4s ASCII-Circuit v1.24.140803 Beta

The .pdf file referenced on the Maplin page doesn't say much about the sensor itself. You have to be careful about installing it in a food service environment, though. This requires some looking into. Another issue might be that the module will have a "bang-bang" output, which means that it turns on the heater when the temp is too high, and turns off when it's too low. There's no proportioning of the output, which might cause pretty major oscillation in liquid temperature -- in fact, it might make it worse than not having any controller at all. If you adjust so the water starts at a certain initial temperature, it may be better to control the temperature of the liquid by just using a lamp dimmer in series with the heater, replacing CRY2 directly in the circuit above, and keeping it at a setting that will keep the temperature fairly stable. You can then use the FE33L as a temp display only. Don't know. Could use some more information here. Or even better, one or two good experiments with tap water before you brew anything.

Hmmn. Home brewry vs. wife -- a difficult choice. I'd have to think 'er over a while. ;-)

Cheers! Chris