Inrush is usually handled by having a resistor of, say, several kohm between the rectified and filtered output of your CT circuit and the AD converter (or the uC if it has built-in ADC). Then a diode to the VCC rail and another to GND (BAV99 is a nice dual diode for that). The white-knuckle approach would be to let the internal substrate diodes take care of things after that resistor, something that's done all the time. Just don't exceed abs max values.
Now if the CT circuit output voltage spikes when a lamp or motor turns on the spike is capped.
In message , dated Thu, 14 Sep 2006, Jim Thompson writes
Well, if you snatched one of those away from a Brit, you'd get plenty of noise. Just ask Genome!
I'm afraid we don't have a proper English word for them; I think we have to use a - horrors! - French word, 'croute'.
--
OOO - Own Opinions Only. Try www.jmwa.demon.co.uk and www.isce.org.uk
There are benefits from being irrational - just ask the square root of 2.
John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK
I would MUCH rather stick with through hole stuff. Those tiny SOT packages are not something I enjoy working with.
So here is where we seem to be at: Choosing between:
500:1 CT TRIAD CSE187L (cheaper)
-=OR=-
1000:1 AMVECO AC-1020 (better choice)
Then using the scematic provided by Jim (If this is what you guys are still talking about)
formatting link
What are the specs I need to be looking for in the bridge?
Again using the provided schematic, the output of the OP-AMP (standard LM-324) will go to through a single 2k resistor that is tied to the input pin of my PIC micro. To be even safer, the net between the output resistor and the PIC should be tied to VCC and GND via reverse biased 1N4148 or similar general purpose diodes?
This leaves me with choosing component values for (from the provided schematic) R1, R2 and C1. Something for which I may need help. But at this point I need to ensure that I am on the same page as those who are helping me. If this is the case, then I can begin to look at the circuit and how the values are derived (so that I fully understand what is going on).
Question: Assuming that I (we) get this all worked out. Will the input pins of the PIC need any caps or other filters to keep them from behaving in a strange manner when not being sampled? I have read that this can be a problem with some uC A/D topologies, as well as Analog multiplexors (a currnet spike on all of the inputs each time the active input is switched to the next pin).
Any old bridge will do. You're dealing in only 10's of mA, and PIV of no more than a few volts.
Wouldn't hurt... will safely limit any fault currents flowing thru the ESD diodes of the PIC.
R1
C1 should be all you need.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I'd add a resistor between C and the PIC. Low enough to make sure the ADC in the PIC works fine (I don't know their input circuitry) and high enough to avoid driving the subtrate diode of the PIC on that input pin past the abs max limit. Probably a few kohm.
You never know which supply comes up first and driving a PIC via a substrate diode might not be a good thing. Although I have seen a schematic where a guy deliberately did that.
Reading comprehension score = 20%, you missed the OP saying...
Again using the provided schematic, the output of the OP-AMP (standard LM-324) will go to through a single 2k resistor that is tied to the input pin of my PIC micro. To be even safer, the net between the output resistor and the PIC should be tied to VCC and GND via reverse biased 1N4148 or similar general purpose diodes?
(;-)
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Are you using a KVM? I'm using an IOGear box with 4-way capability.
...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
I would probably go for something cheap in a 1 A, 50 V bridge, like http://59.120.39.77/mccsemi/up_pdf/DB101-DB107(DB-1).pdf about $.50 each from Digikey. It drops about .7 volts at the current you will be shoving through it. Of course, you can probably find 1 A
50V axial diodes for about a nickel each. You could also use 4 1N4148 switching diodes that are rated .15 A at 75 for less than that.
If you want to add an extra over voltage clamp to cover an open bridge diode, you might use a pair of 1N4734A, 5.6V 1W zeners in series opposing, about $.10 ea.
Only the Barricade router (probably the same that you have) plus another switch and a printer multiplexer. But when doing filters I use PC#1 (w/ left-hand mouse) for one program and PC#2 (w/ right-hand mouse) for another or for sims and CAD. Then the window on PC#1 overlaps into the NG window. I still shouldn't have missed that paragraph.
BTW, in case you ever have to do wave digital filters because there is no real estate for a full multiplier: TI just came out with a DOS calculator for the coeffs. Called "wdf_coeff.exe" and comes with the zip files in app note slaa331. It evens spits out the coefficients in CSD so it doesn't have to be done by hand. Sweet.
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
It's a distant cousin twice removed of the IIR family :-)
These come in really handy if you have to do baseband filtering and the real estate is tight. Their main advantage besides stability is that you can butcher their coefficients a little without too much in pass-band penalties (but you do have to keep an eye on the stop-band). IOW when trying to get away with the least amount of "ones" in them. Since subtraction is as easy as addition you can also replace some of them with "-1" which often further reduces the load. For uC guys the positions of the "1" or "-1" will determine the number of shift operations needed to get to each add/subtract while for the chip designer it's merely a routing matter. Darn, you guys always have a leg up when it comes to implementing stuff.
Sadly, I do not have a scope yet. I would not even know how to utilize one. That is surely something that is hard to self learn. I keep an eye out on eBay for cheap units but honestly don't really know what to look for. I also play around with audio stuff as well. It does however appear that this is a tool I am going to need to invest in to further my knowledge and understanding of circuits such as this.
I am going to try and get this simple circuit breadboarded ASAP and see if how well I can implement it. I just purchased a PIC book today, as that appears to be the easiest way for me to sample the data and then async it to the PC as needed.
I feel (and know) I am much closer to understanding this project and being able to move forward to actually realizing a working prototype. Thanks!
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems | manus |
| Phoenix, Arizona Voice:(480)460-2350 | |
| E-mail Address at Website Fax:(480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |
I love to cook with wine. Sometimes I even put it in the food.
Almost anything is better than nothing, and scopes have been going for peanuts on eBay US recently.
A basic scope is 5 MHz. A good one is 20 MHz and a great one is 100 MHz. Dual channels are nice, and a delay on the sweep is very nice indeed (looks like a 10 turn pot).
Just make sure it works some - a focusable trace is a good indicator. You sure don't want to try to find a new tube.
I looked several years ago, but was afraid to purcase something that I was not sure of. I started out looking 5MHz stuff and ended up looking at 100MHz stuff. I gave up in frustration and lack of the most basic ability to choose a good used unit. I have shelfs full of impulse eBay buys that I did not research well.
Here is what I gather my circuit is suposed to look like:
formatting link
Here is what I understand that needs to be done (In the event I have made no errors).
1) I am still unsure of the best choice for the CT (the 500:1 Triad, or the 1000:1 Avemco)
2) the choice of CT will dictate the size of R1
3) Once R1 is calculated, then R2 needs to be selected to provide the A/D with a suitable voltage range.
4) The value of R2/R1 gives the Amplification ratio of the inverting amplifier that is formed by the OP-AMP. In this case it would be 7.87. So 1mv on the output of the Bridge will provide 7.87mV to the D/A through R3. 10mV would provide 78.7mV. and 100mV would provide 787mv?
5) The inverting amp is being fed from the negative side of the bridge, so the output of the amp will be a positive voltage?
6) I think I have the diodes oriented correctly to protect the A/D input pin from the transients. The more I look at them the more I doubt myself. I thought I understood what was going on here.
7) From the datasheets I see that the recomended BAV99 package is faster and has a lower capacitance than the through hole 1n4148s I chose. I hope this is not an issue for the intended purpose, as I am not good with SOTs and certainly don't want to do 24 of them at 3 pins each!
If I am totaly off base, please let me know and I will give this up and buy more electronics books before I waste anybody elses time.
Lastly: There will be 24 of these in my house running 24/7. After the numerous open secondary warnings, is there anything else that I need to do to ensure safety for myself and our home? Honestly, after all of the grave warnings, I actually feel like (in comparisson) that the act of poking around the grid voltage and gain stages of my tube amps is safe!
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