Question re:FCD {EDIT: post added- new problem}

stipro · Post by **stipro** » Sun Mar 05, 2006 5:42 am

I finally got around to testing the FCD that I built. I used my computer power supply, as mentioned. After going full sweep on the potentiometer, the output voltage is only 1.1 volts. Is this ok?

vrg3 · Post by **vrg3** » Sun Mar 05, 2006 5:54 am

No. It should get up to around 4 volts.

Did the output track the input up until 1.1 volts?

Did you by any chance use a 4.7K resistor instead of the 47K resistor?

stipro · Post by **stipro** » Sun Mar 05, 2006 6:32 am

vrg3 wrote:No. It should get up to around 4 volts.

Did the output track the input up until 1.1 volts?

Yes, the output voltage increased with the the input voltage. But the potentiometer was only turned 1/3 of the way before it was maxed out(1 turn pot) . The last 2/3, the voltage on the output did not increase. As for the resistor, I am certain that I used a 47k. I will have to check to be absolutely sure.

vrg3 · Post by **vrg3** » Sun Mar 05, 2006 6:48 am

Hrm.

Use a 100K resistor instead of the 10K then, maybe?

stipro · Post by **stipro** » Sun Mar 05, 2006 7:22 am

Well unfortunatly for me I set it in epoxy before testing it. So this means having to collect parts to build another one. Unless you have a spare one lying around you wouldnt mind be rid of

.

stipro · Post by **stipro** » Wed Mar 08, 2006 5:13 am

OK. what gives? I built a new FCD tonight and set out to test it as I did the last one that failed the voltage test, onlt this time it was even worse. Last time I maxed out the voltage at 1.11 volts, this time the voltage maxed out at 0.1volts. The wiring is correct, aswell as the resistors, diode direction, and chip set. This is driving me bonkers. What gives?

If I hook up +12volt power and the 5volt source(4.95 volts from my pc), without a ground, I get 5.76volts on the output, but when I hook up he ground, voltage sits at 0.1volts.

I will try and get some pics up when the thawagallery is up and running again, in the mean time an ideas?

Thankx.

vrg3 · Post by **vrg3** » Wed Mar 08, 2006 4:05 pm

Hmm, I'm puzzled.

How exactly are you testing it? Something like this?

Yellow wire from PC power supply to +12v on FCD.
Red wire from PC power supply to +5v on FCD.
Black wire from PC power supply to ground on FCD.
Potentiometer (at least 1K) across red and black wires, with wiper going to input on FCD.

It doesn't make any sense to test this circuit without a ground. The results don't really tell you anything.

stipro · Post by **stipro** » Wed Mar 08, 2006 11:49 pm

vrg3 wrote:How exactly are you testing it? Something like this?

Yellow wire from PC power supply to +12v on FCD.
Red wire from PC power supply to +5v on FCD.
Black wire from PC power supply to ground on FCD.
Potentiometer (at least 1K) across red and black wires, with wiper going to input on FCD.

That is exactly how I am testing it. With the wiper on the pot is turned right down(off position) the voltage at the output reads 0.1. When I turn the pot to max, the voltage does not change. I dont know, could the chip be buggered. Iam not complaining, I just want to get this figured out, and right.

Thanks for your time Vikash, I really appreciate it.

vrg3 · Post by **vrg3** » Thu Mar 09, 2006 2:54 am

Glad to try to help...

This is very weird. That's exactly how I test them too...

It's a remote possibility, I guess, that you found a bad batch of LM224s... Never heard of that happening before though.

You're taking appropriate precautions against electrostatic discharge?

I don't know what to tell you. Bad pot? Have you measured the voltage at the input to the FCD to make sure it's varying from 0 to 5 volts?

stipro · Post by **stipro** » Thu Mar 09, 2006 6:09 am

vrg3 wrote:Have you measured the voltage at the input to the FCD to make sure it's varying from 0 to 5 volts?

Yes, it definately does that. The wiper on the pot, and the input voltage, sweeps from 0 to 5 volts. Ok, but here is the weird part, with the pot still hooked up, but turned off I still get 0.11volts at the output. With the pot at max, still 0.11 volts.

There is no change in output voltage relative to any input voltage. Its like there is some wierd connection.

(At least on the first FCD I built, the output voltage went up to 1.1volts before being clamped)

I wish I could get a video for you. As they say a picture is worth a thousand words.

BTW-the pot is a 20k

vrg3 · Post by **vrg3** » Thu Mar 09, 2006 4:12 pm

Hm.

A picture of the circuit might help me see if you did anything wrong in assembling it... But it does sound like you know what you're doing.

Okay... so let me list a bunch of checks that you can do:

- Voltage at pin 5 varies between 0 and 5 as you turn the pot. (You already did this one)
- Voltage at pin 4 is about 12.
- Continuity from pin 11 to ground.
- Voltage at pin 10 is about 4.
- Voltage at pin 8 is about 4.
- Voltage at pin 7 is about the same as the input.
- Voltage at pin 12 is about the same as the input except it's never higher than about 4.

Try each of those checks and let's see which ones fail.

stipro · Post by **stipro** » Fri Mar 10, 2006 12:37 am

Here is what I found.....

vrg3 wrote: Voltage at pin 4 is about 12..

check

vrg3 wrote: Continuity from pin 11 to ground..

check.

vrg3 wrote:- Voltage at pin 10 is about 4..

check

vrg3 wrote:- Voltage at pin 8 is about 4..

Not even close. Its at 0.02volts

vrg3 wrote:- Voltage at pin 7 is about the same as the input..

Voltage here is 0.1volts

vrg3 wrote:- Voltage at pin 12 is about the same as the input except it's never higher than about 4..

And voltage here, is 0.1volts

So in conjuction to all these tests I would say that this particular LM224 is junk.

What do you think?

vrg3 · Post by **vrg3** » Fri Mar 10, 2006 4:36 am

Wait, maybe it's a bad diode.

Disconnect the cathode of the diode from pin 8 of the LM224 and then measure the voltage at pin 8.

biggreen96 · Post by **biggreen96** » Wed Jun 14, 2006 11:16 pm

I just put a FCD together and would like to test it, I dont have a pot though. Is there any other way? I have a power supply and a voltage meter thing.

vrg3 · Post by **vrg3** » Thu Jun 15, 2006 12:53 am

Make a pot. Take a piece of paper and draw a line across it with a pencil. Check the resistance of the line (put the multimeter's probes at the ends of the line); you want it to be somewhere between maybe 1K and 100K, so adjust the length of the line to achieve this.

Then you connect +5v to one end of the line, ground to the other end of the line, and touch the FCD's input wire somewhere in the middle of the line.

stipro · Post by **stipro** » Thu Jun 15, 2006 1:02 am

vrg3 wrote:Make a pot. Take a piece of paper and draw a line across it with a pencil. Check the resistance of the line (put the multimeter's probes at the ends of the line); you want it to be somewhere between maybe 1K and 100K, so adjust the length of the line to achieve this.

Then you connect +5v to one end of the line, ground to the other end of the line, and touch the FCD's input wire somewhere in the middle of the line.

Does that really work? If so that is super cool

.

vrg3 · Post by **vrg3** » Thu Jun 15, 2006 1:15 am

Sure it'll work. You just tape the wires on the ends down.

free5ty1e · Post by **free5ty1e** » Thu Jun 15, 2006 2:16 am

Gotta love the ghetto style pot.... unless of course you're talking about actual pot, in which case the ghetto stuff isn't so good

Seriously though that's a cool way to do that... I never though of using a pencil line

Edit -- if you guys don't feel like messing around with your FCDs anymore I'll have some for sale very soon.

http://bbs.legacycentral.org/viewtopic. ... &start=100

biggreen96 · Post by **biggreen96** » Thu Jun 15, 2006 9:39 pm

ok so I did something incorrectly. I connected the ground to my PC plug, then I connected the +12v and the PC turns itself off. I assume to protect it.

The little yellow thing (1uF on the diagram) does that have to be installed a certain way? I just dropped it in there willy-nilly, same with the 1N4148 thingy.

biggreen96 · Post by **biggreen96** » Fri Jun 16, 2006 3:03 am

ok so I flipped the little yellow guy around (1uF) and that seems to work. Right now with just the +12v, ground and +5v connected I read 4.16v. Should the output be ouputing anything without anything connected to the input?

-chris

vrg3 · Post by **vrg3** » Fri Jun 16, 2006 3:56 am

PC power supplies are pretty good about shutting down if you try to draw too much current, so it does sound like you shorted it out.

The 1uF capacitor may need to go in a particular direction depending on what type it is. On the types where it matters, there's a marking of some type on the capacitor, usually marking the side that goes to ground with a minus sign or something.

Usually getting the cap's polarity wrong just causes it to eventually fail (sometimes spectacularly); I've never heard of it causing a short circuit like this. More likely the capacitor presented just a little too much load for the power supply the first time around -- technically it acts like a short circuit for a tiny fraction of a second. Is your PC power supply a high-quality one from a brand name? If it continues to have problems with this, just remove the cap while you're testing. In any case, your car will have no problem with it.

The 1N4148 diode absolutely has to go in a particular direction -- the stripe on the diode should be on the end connected to pin 8 of the chip.

The circuit will always output something; it's just not predictable or relevant if nothing's connected to the input.

biggreen96 · Post by **biggreen96** » Sat Jun 17, 2006 1:05 am

I bought a pot, the guys at the radio shack had no idea which one i needed so I bought a linear taper 250vdc .25W pot. I guessed on hooking it up, since there were no instructions. well it started smoking. hehe this stuff is fun. what kind of pot should i get when i go back to the store?

free5ty1e · Post by **free5ty1e** » Sat Jun 17, 2006 1:31 am

your pot started smoking itself? That's a new one.

Did you say 250 volts DC??

biggreen96 · Post by **biggreen96** » Sat Jun 17, 2006 1:47 am

yeah thats what it says on the packaging.

vrg3 · Post by **vrg3** » Sat Jun 17, 2006 3:41 am

It sounds like it was too low a resistance. What was the resistance of the pot?

If you're buying one from Radio Shack I would suggest something like 271-1716 or 271-092.

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Question re:FCD {EDIT: post added- new problem}

Question re:FCD {EDIT: post added- new problem}