looking for a 555 timer circuit

No, S1 _is_ normally open and, by convention, (since it's common knowledge and available on the data sheets) we usually don't show the power connections, or we tabulate them on the drawing. Guess I should have made a table!

Anyway, here it is:

-------+------+-----+----- U1 7555 8 1 U2 HC175 14 7 U3 HC02 14 7 U4 HC4060 16 8

Also not shown are the 0.1µF bypass capacitors that it's considered "good practice" to install between Vcc and ground on each chip. Cheap ceramics are fine.

I've built the circuit and I'm testing it now. Right now, all three outputs are high and stay high (>2V) until I press the reset button, at which time they all go low. I haven't waited the 30+ minutes yet after resetting to see what would happen. I've double-checked all of my connections and made sure I have what is shown in revB plus the changes you mentioned earlier. I'm using a 5V DV power supply.

I'm looking at the data sheet for the 4060, and it's not matching what you have in the schematic: Q11 doesn't exist on the data sheet (I've looked at 3), and Q6 is on pin 4, not 6. I'm trying to figure out how the 4060 works, but haven't yet. What should Q11 actually be?

--- Did you make the changes I outlined in my last post:

"In going over the circuit for the last time, (LOL) I found a few errors:

1. U2-5 should be connected to U1-3, not U1-1
2. C1 should be an 0.18µF polyester cap.
3. R1 should be a standard 2 megohm +/- 5% 1/4W carbon film resistor."?

In either case, it should be working, but if you didn't make the changes the timing will be off.

I don't understand whether you're saying that it doesn't work at all, or whether you're saying that you don't know whether it's working properly because you haven't waited the half-hour or so to make sure whether it's working or not.

In any case, to start troubleshooting it, disconnect it from the DC supply and disconnect all of the loads. Then set R2 to its halfway point and reconnect the supply. You should see a 5VDC square wave with a period of 1/2 s (2Hz) on U1-7.

If that works, then the oscillator and the first three stages of the internal divider chain in the 4060 are working. If it isn't, then there's a wiring error or a bad chip somewhere. Also, if you press the PAUSE switch, all of U1's outputs should go low for as long as the switch is pressed. After it's released, pin 7 should toggle at

Try it and post back with what you find and what kind of test equipment you have available, and we can devise a troubleshooting plan.

BTW, if U3 comes up with the outputs all high, (which is entirely possible and doesn't indicate an error of any kind) that means that all three pumps will run at the same time for 30 seconds when you first power up, after which they'll drop into their normal sequential, mutually-exclusive mode. If that's a problem we can use the spare gate, a resistor, and a capacitor to build a power-on-reset which will guarantee that the U3's outputs come up all low whether you press the PAUSE switch or not. Would you like to do that?

-- John Fields Professional Circuit Designer

Ok. The only test equipment I have is a digital autoranging multimeter. I don't know if you saw my other post below, but the 4060 pinout is different than the 4040, and does not have a Q11 output. Q6 is on pin 4, so I changed that. I used Q12 for now instead of Q11.

What I'm seeing now: Pin 9 on U3 (HC175) is cycling from 0V to 5V every 8 seconds or so. Pin 2 on U3 (HC175) is cycling from 0V to 2.2V at a large time interval (unsure how long, but greater than 30 seconds), maybe due to me using Q12 on U1 (4060). I have not observed Pin 7 or 10 on U3 switching states. I'm double checking my wiring again to make sure I haven't missed something.

Would me using Q12 on U1 cause any problems other than a longer on/off time?

--- Yes, I explained that lack of naming consistency between manufacturers in an earlier post. Regardless of the names used for the outputs, the pin numbers I called out on the schematic (modified by the post I made about the error I made) are correct.

Here's the essence of the post:

" In going over the circuit for the last time, (LOL) I found a few errors:

1. U2-5 should be connected to U1-3, not U1-1

1. C1 should be an 0.18µF polyester cap.

2. R1 should be a standard 2 megohm +/- 5% 1/4W carbon film resistor."

---

---

It's a ripple counter with an on-board oscillator _ _ _ _ _ _ _ _ _ _ _ CP _| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_| |_ ___ ___ ___ ___ ___ _ Q0 ___| |___| |___| |___| |___| |___| _______ _______ _____ Q1 _______| |_______| |_______| _______________ Q2________________| |_____________ _____________ Q3________________________________|

and so on...

---

--- Depends on whose data sheet you've got. Which one is it?

-- John Fields Professional Circuit Designer

An U1-7 is cycling, don't know if it's 2Hz, but it is cycling.

I couldn't find the datasheet for the 4060 I have: The number on the chip is SCL4060BE with a picture of a cube with 'S' on each side of the cube.

--- OK, here's a link to the data sheet I used:

and a link to the final schematic:

news:// snipped-for-privacy@4ax.com

If everything works like it should, whenever you power up or hit the PAUSE switch, U3Q1, Q2, and Q3 should go low and stay low until U1-3 goes low. That should be about 30 minutes with the pot set at mid-range. During that time, U2-10 should be low, U2-4 should be high, and the outputs of U10 should be toggling, with U1-7 exhibiting a period of 4 seconds (two seconds high and two seconds low).

When U1-3 goes high, the reset will be taken off of U3, and 30 seconds later its 3 phase output cycle will begin with U3-2 going high.

-- John Fields Professional Circuit Designer

I've made the modifications except for the C2 in the revision C (have to go get one). I still have not managed to find what I have wrong at this point. Right now, U3Q1 seems to be staying high (2.2V) and I have not observed U3Q2 or U3Q3 switching. U1-7 does exhibit a period of 4 seconds as you mentioned, and U1-6 does toggle.

Yes, that happens.

I'm starting to think that U3 is bad, though. I see the clock on pin

On U2, Pin 1 is 5V, Pin 2 is 2.2V, pin 3 is 0v.

If I'm understanding the logic correctly, every time the clock goes low to high on U3 pin 9, the output should change: Q1 -> Q2 -> Q3.

Any thoughts?

Also, I still can't figure out why I have a difference in voltages. Shouldn't I have ~5V across the board? Could this be part of the problem?

MM74C02N is the part number on the chip.

--- OK.

If U3-1 is high, and U3-9 is toggling, then U3-2 should be either low (close to 0V) or high (close to +5V), depending on where in the three phase cycle U3 happens to be.

That 2.2V is the problem, and since it's on U2-2, U3-2 and U3-5, that indicates that those three points are connected, like they should be. In my experience, a voltage on a CMOS output about halfway between Vcc and GND more often than not indicates a high output shorted to a low output. If that's the case, then the chip(s) involved in the short should feel warmer than normal, which is anything other than cool to the touch.

What I'd do is to go over the wiring one more time, making sure I didn't have an extra wire in there going somewhere it wasn't supposed to, or a solder bridge creating a short, or maybe even a burned or cut wire with the exposed conductor touching something it wasn't supposed to.

If that doesn't help, then I'd disconnect the wire(s) going from U3-2 to U2-2 and U3-5, connect U2-2 and U3-5 to ground, power up, and hit the pause switch. U3-2 should wind up low, and if it comes up high or at 2.2V then U3 is bad.

If it comes up low, then the trouble lies somewhere else and we'll have to run some more tests to find out where it is. Post back with what you find and we'll take it from there...

-- John Fields Professional Circuit Designer

What's the difference between a 74C02 and a 74HC02? My local store didn't have the 74HC02 in stock, so I got the 74C02.