Actually, I have a quesion that "rezer" mentioned above. He states to use the "non-inverted" as the "input". What actually are you considering as the "input". Is this the "referance" signal of 3.3V.....Or the signal that changes from the 2V to 5V for the trigger.?
Pin #2 of the LM311 is called the "non-inverted" pin. This is where I have the "trigger" signal coming in.
Also, I did not read through the post, you state that I should switch the 240 ohm to a 2K ohm to reduce current. I did not do that. Is this a possible cause? Are my 2 pins reversed for Pin #2 and Pin #3?
Stu
OK, might need a bit more help here. I totally benched tested the circuit board and it worked OK. I have exactly 3.3v as the referance. I inputed approx 2.7v and it did not trigger. I then applied about 4.3 V and it triggered. My problem now is that when it is all installed in my car, the coil is "hot", or "on". If all is right, the coil should not be triggering until it gets its 5V signal. Here is one possibility. I measured the input referance voltage in my car, and it was not 2.5V at idle, it was 1.9V....In further testing, I am getting a reading 7.3V on the TIP31 Collector to Coil (Pin 85). Now if the output of the TIP31 "is" triggered, shouldnt that be 12-13V? Why am I getting 7.3V.........and why am I getting "any" voltage at all if it isnt supposed to be triggered until the car gets to 5V +/-?? What could I be missing? What is the typical voltage for an automotive 12V relay at the coil in order to trigger it? Would 7.3V be enough to turn the relay on.
Maybe I have a bad relay.........cause it kind of hums a little.
Thanks for the help.
This statement confuses me. At 2.0V (+/-), I DO NOT want the relay coil energized. I want it OFF so it is using "Input A" for the fuel pump supply voltage. I want the TIP31 to turn "ON" and energise the coil when the input signal jumps to 5V (+/-). This might be where we are confused on the (+) (-) non-inverted thing.The TIP31 will turn on at 1.8V and the LM311 has a Vsat of .75V,
This statement confuses me. At 2.0V (+/-), I DO NOT want the relay coil energized. I want it OFF so it is using "Input A" for the fuel pump supply voltage. I want the TIP31 to turn "ON" and energise the coil when the input signal jumps to 5V (+/-). This might be where we are confused on the (+) (-) non-inverted thing.
Oops! I calculated your current sink off of the Vsat of the LP339, not the LM311. Also, your alternator will run at around 14V, not 12V. Isink is 55.2mA. You are over-driving the LM311. Replace the 220Ω with a 470Ω.
Actually, maybe I have the inputs backwards. It keeps getting switched around. So I need to be clear on which pin is the "ref" (3.3v) and which pin gets the dual voltage signal. First drawing had one way, and your latest had it reversed. Maybe this is the possible problem?
I have it now, Pin #3 called the "Invert" is getting the 3.3v ref. V. Pin #2 called "non-Invert" is getting the dual input voltages (2.5 to 5.0V) Not sure which one needs to be the (+) or (-) if it really matters.
Stu
I will explain my operation again just so we are all on the same page.
1) The typical operation outputs a 2.0V signal to run the FP at 9V.
2) The "trigger" voltage that tells the onboard ECU to go to 12V is a 4.5 +/- V Signal.
So I want the comparator to do nothing.."off".. when it is at the 9V state, or a constant 2.0V signal. I want the comparator to switch to "on" state when it gets that 4.5V Signal.
Tonight, I fed the PIN#2 (+) terminal a 4.5V signal, and the OEM computer did in fact kick the output to 12V from 9V. But the output of the comparator did not fire the relay. In either case, I read 12V at both sides of the relay coil. I did not measure the output Pin#7 on the comparator. I can do that. But whatever it is, it isnt triggering the relay.
Here is a quote from a comparator design notebook. Hence why I ask about the (-) and (+) Terminals. According to the below, I need to do the reverse because by reference is 3.3V and my input trigger "on" is about 4.5V. So if my "ref" is 3.3V that is "lower" than my trigger of 4.5V. Whereas the "off" state is where my "ref" of 3.3V (+) is now "higher" than the "input" (-) of 2.0V
Input Vs. Output Results
Current WILL flow through the open collector when the voltage at the PLUS input is lower than the voltage at the MINUS input.
Current WILL NOT flow through the open collector when the voltage at the PLUS input is higher than the voltage at the MINUS input.
I tried switching based on the above, and it still is not working.
Odd thing a few days ago, I could get the relay to "click" on when bench testing.
I will take more V readings. I will also put back the 240 ohm resistor to see if that helps as well.
I have taken it back out of my car to do further bench testing. It is very possible I did damage the circuit because it got wired incorrectly into my car on the first attempt. I may just etch a new one since I have extra parts.
Out of curiousity, is it important that I wire both V(-) and Ground together? Can I just use Ground to car chassis ground and not ground the V(-) pin? Or should I jumper these 2 pins (#1 and #4) together as the diagrams show?
The only other possibility is that I have not installed the "snubber" circuit accross the relay pins. Woulld that solve all my problems? If not, I don't know why it works fine on the bench, but not in the car. Only difference that I can see is that the car has a higher voltage than what my bench generator supplies. Last night, when I had the 470 ohm resistor in, it just didnt work at all, and both sides of the relay had 12V. And I could "not" get it to trigger at 4.5V. Now, because it is occillating so bad It can't trigger. Problem, is how do I stop this from happeing?
Stu
Here is a typical data sheet for the relay type I am using. "Type F" 12VDC
Min. Operating V of 7.x. Release Min 1.2V 90 ohm coil. Automotive. (Don't know why they show a resistor accross the coils as an optioninal thing)
https://www.electro-tech-online.com/custompdfs/2008/09/VF420cat20pages-1.pdf
At initial start up I see about 14-14.3V at idle. It eventually settles down to about 13.2V.
I do not have a scope...The above should suffice for the relay data. I can take a pic of the board, but I will upload my etch layout. This is looking from the circuit path side. This is how I made the board.
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