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Need Help Wiring a load Fault Indicator

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Yes I thought you meant all my voltages but here they are anyways...
7805
1. 14.02 vdc - Fine.
2. 0 - Fine.
3. 4.94 vdc - Fine.

Opamp
1. 2.5vdc - High. This should be approx. 1.6 Vdc or less (with 43.9 mVdc on pin 4)

2. 43.9mv - OK. The V level from the shunt

3. 3.4mv - The comparator bias. This is low. It should be approx. 7.5 mVdv it will still work.

4. 0 - Gnd.

5. 3.5mv - lso low, but should work.

6. -0.2mv - shunt value, although I would never expect to see a negative value. Might just be the meter.

7. 2.5vdc - #2 comparator output, and with a 0 V value on pin 6 this should have a voltage level of approx. 3.2 Vdc.

8. 4.97vdc - OK. Vcc

If you were to ground, for example, pin 2 (for example, to Pin #2 of the 7805), the LED on pin 1 should turn ON. Allowing pin 2 to return the value off of the shunt should turn it off.

Try putting a 270 Ohm resistor between both pins 2 and 6 (the inverting inputs) and circuit ground:
Invert bias.JPG

This is to bias those inputs to ground when the shunt voltage floats.
 
7805
1. 14.02 vdc - Fine.
2. 0 - Fine.
3. 4.94 vdc - Fine.

Opamp
1. 2.5vdc - High. This should be approx. 1.6 Vdc or less (with 43.9 mVdc on pin 4)

2. 43.9mv - OK. The V level from the shunt

3. 3.4mv - The comparator bias. This is low. It should be approx. 7.5 mVdv it will still work.

4. 0 - Gnd.

5. 3.5mv - lso low, but should work.

6. -0.2mv - shunt value, although I would never expect to see a negative value. Might just be the meter.

7. 2.5vdc - #2 comparator output, and with a 0 V value on pin 6 this should have a voltage level of approx. 3.2 Vdc.

8. 4.97vdc - OK. Vcc

If you were to ground, for example, pin 2 (for example, to Pin #2 of the 7805), the LED on pin 1 should turn ON. Allowing pin 2 to return the value off of the shunt should turn it off.

Try putting a 270 Ohm resistor between both pins 2 and 6 (the inverting inputs) and circuit ground:
View attachment 84702
This is to bias those inputs to ground when the shunt voltage floats.
Applied resistors it had no effect. Also is it possible i might have got this op amp in upside down? There was a indented circle on the top left in the plastic which i just assumed was pin # 1. Could this op amp be defective like the regulator? Is there any way of troubleshooting that? attatched a pic of what it looks like so i didnt have the 270 resistors on 2&6 yet.
 

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Trent,

Thanks for the pic. And I now see the problem. And I'm afraid it's partially mostly my fault. I made some assumptions that were in error.

The TL082 is a dual OpAmp package:
TL082 Pinout.JPG

Note pinout numbering and description.

The schematic I provided was a representative diagram for only ONE of the two OpAmps in a TL082 and the pin numbering used in the schematic are irrevelant (read WRONG) for the actual wiring of the chip. This is an artifact of the SIM Spice model I have for the TL082.

I will post an amended wiring diagram shortly...

My apologies for this mistake.

CBB
 
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Here's the correct schematic for the TL082 Dual Comparator circuit you need:
TL082 Dual Comparator.JPG


<EDIT> I think it's best to build the circuit without shortcuts. Using a larger PCB might also be a good idea, at least for the prototype.

I would suggest that the PCB for this circuit be placed as near as possible to the LEDs (inside the vehicle). Might also be a good idea to use an 8 pin DIP socket for holding the TL082 chip (makes it a lot easier to replace, should that be necessary).

Also, should the chip not have a dimple or dot (indicating pin1, as you correctly surmised), there will be a "notch" at one end. In that case, pin 1 is indicated below (looking at the TOP of the chip):

Pin 1-->
Chip Pin 1.JPG


Again, sorry for any misunderstandings.

CBB
 
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Here's the correct schematic for the TL082 Dual Comparator circuit you need:
View attachment 84706

<EDIT> I think it's best to build the circuit without shortcuts. Using a larger PCB might also be a good idea, at least for the prototype.

I would suggest that the PCB for this circuit be placed as near as possible to the LEDs (inside the vehicle). Might also be a good idea to use an 8 pin DIP socket for holding the TL082 chip (makes it a lot easier to replace, should that be necessary).

Also, should the chip not have a dimple or dot (indicating pin1, as you correctly surmised), there will be a "notch" at one end. In that case, pin 1 is indicated below (looking at the TOP of the chip):

Pin 1-->View attachment 84707

Again, sorry for any misunderstandings.

CBB
Built this again new parts new resistors to your schematic and the new one does the exact same thing LED's constantly on same readings as before
 
Ok.

Try this.

Everything powered OFF.

Disconnect the fan shunt lead from pin 2. Power up the TL082 circuit. Presumably LED1 is ON.

If so, momentarily jumper from pin 1 (5 vDC) to pin 2 of the TL082. Does LED1 go OFF?

I'll wait if you're still on-line.

<EDIT> Trent, I know this is frustrating, but the circuit works. Just trying to determine why it's behaving the way it is...
 
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Ok.

Try this.

Everything powered OFF.

Disconnect the fan shunt lead from pin 2. Power up the TL082 circuit. Presumably LED1 is ON.

If so, momentarily jumper from pin 1 (5 vDC) to pin 2 of the TL082. Does LED1 go OFF?

I'll wait if you're still on-line.
No but it does dim the LED by at least half
 
Ok.

I know this is frustrating, but bear with me.

Fan shunt still disconnected. Jumper from pin 8 to pin 2. What does the LED do?
 
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Ok.

Soemthing is, obviously, not right.

I gotta hit the sack.
One last thing, if you would - measure the voltage on pin 1 with and then without the jumper from pin 8 to pin 2 and post those values. At this point I suspect it wont be that different, and that's the problem.
I'm going to breadboard the circuit tomorrow AM and confirm. The SIM says "fine" but...

Ain't electronics FUN!! :banghead: :banghead: :banghead:
 
2.21vdc with jumper and without

Not good. I'll post my results with the circuit today.

Would it make a difference if i used 1/2 watt resistors or 1/4 watt but still the same resistances?
No. The power dissipating rating (wattage) of the resistors has no effect on the operation of the circuit unless exceeded. In that case the resulting overheating of the resisitor can (and will) alter the resistors's value.[/quote]
 
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Trent,

I couldn't get the "real" circuit to work, either.

First time the SIM I use (Texas Instruments) has failed me so spectacularly.

I'm working on a new design (a so called "window comparator": it uses both OpAmps of theTL082 per fan).

The basic concept for your fan failure circuit is sound. It's just the implementation that kicking my butt.

Again, I'll post something as soon as I'm sure that in the real world it'll work... :woot:.
 
CBB:

You only have a snowball's chance to get this to work. The TL082 is NOT a single supply OP amp. Remember you can do a quick test setting it up as a unity gain buffer. ( - to out ) and (+ to ground ). Measure out: should be near zero. Measure the difference between - and +: Should be near zero.
 
Thanks, KISS.

I knew I was pushing the envelope. Surprising to me the SIM let me do it. Obviously wise to dump the TL082 - was just trying to keep the part getting to RS.

Theere's a good 45-50mVdc sig from the downstream side of the fan when it's operating. A fan failure let's that value go to Gnd (I been led to believe the fan is switched from the + side). I figured with a comparator with an inverted output, with a threshold of something around 35mV would do the trick. Like I say, the SIM led me to believe I could.

Got any ideas? I've already got 18 hrs into this and I feel somewhat obligated (especially since he's spent some USDs on it already) to help the OP.

Not too big to admit defeat, though...

CBB
 
First, you need to sing a single supply OP amp or comparitor. Not sure where you shunt figures in and not sure if your OP amp/comparator needs to be rail to rail. All of that usually causes a lot of grief.

If it were me, I think I would start with a version of these: http://www.robotshop.com/en/pololu-...google&utm_medium=base&utm_campaign=GoogleUSA

then most of the "crap" goes away. #1, you get an isolated high level voltage proportional to current to deal with. The nice little PCB is already made up for you too. Note that some sensors are bipolar and some unipolar. It would be "nice" if the sensor output is at one-half 5 Volts, so you already have a signal not anywhere near the rails.

It's HARD to select an OP amp that operates very close to the + or - rail and rail to rail doesn;t necessarily mean it will exactly reach the supply voltage.

See: http://www.analog.com/static/imported-files/tutorials/MT-068.pdf

So there are IC's that CAN amplify a small signal with a high common mode voltage greater than the power supply, usually by a fixed amount. You have similar issues when trying to amplify signals within mV of ground and your reference is ground. Stuff works much nicer with dual supplies.

Radio-Shack used to and may still have the LM339 quad comparator http://support.radioshack.com/support_america/9006266.pdf, BUT the input has to be above 700 mV for the comparator to SEE it.
 
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Thanks, KISS.

I'll check out your links.

I have considered amplifying the shunt voltage (gain of, say 40-50), while considering noise issues/problems: probably have to filter it really well.

Live and learn.

Trent, hope you haven't given up on me. Although, wouldn't blame you if you did...
 
Thanks, KISS.

I'll check out your links.

I have considered amplifying the shunt voltage (gain of, say 40-50), while considering noise issues/problems: probably have to filter it really well.

Live and learn.

Trent, hope you haven't given up on me. Although, wouldn't blame you if you did...
Actually i went ahead and wired the entire thing with both fans and the relay and the first led when both fans are running is out but the second one is on then when the 210f stat is triggered then the led comes on. So wjhen both are running pin one voltage is at 1.9vdc
 
At half speed run in series led one runs trough 2 shunts.... maybe making them 3feet long? Also what would happen if you increased the resistor rating from the led to a higher ohm? Wouldnt that drop the voltage? i can post pin voltages but when both fans are running at low speed the voltsges are really close to what you said they need to be
 
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