Using a 0-5VDC signal towith preset to trigger an n25 opto

[TheEquineFencer]

OK, here's the idea. I am looking at a WideBand O2 monitor. It has a digital readout plus it has a 0-5VDC output for use to connect to an external ECM for an engine. The manufactor says I cannot use the 0-5VDC programmable anolog signal to power anything, but I think it is possible. What I want to do is figure out a way to do it. I know it has to be able to handle some kind of load in the lower Milliamp range. I'm thinking if I figure out how to take the 12-15VDC power source, (battery/alernator from car), regulate a 5VDC and feed it to something like a LM339 with a potentiometer, that way I could adjust the trigger point based on the analog signal from the WBO2 monitor, then feed the LM339 output signal it to a N25 opto and let it do the main switching for any other device I want to power off the analog signal. The 0-5VDC analog signal is equal to 10/1-20/1 Air/fuel ratio and the anaolg output can be programmed for a lineiar slope. I realise I'll need to use the same ground referance point for the whole system or I might get off because of a voltage rise accross the ground path. I'm still learning this stuff so don't feel bad over simplifying something. I have a good grasp on some of this, better than the average Joe off the street. I guess I need to figure out what Zener diode will work for a regulator and how to build a comparator circuit like I need. Feel free to jump in, thanks, Floyd

 

[Reloadron]

The 0-5VDC analog signal is equal to 10/1-20/1 Air/fuel ratio and the anaolg output can be programmed for a lineiar slope.

Hi Floyd

What you have in mind should work just fine. Many indicating device pieces to test, measurement and diagnostic equipment provide an analog voltage or current output that is a value scaled to their indicated value. I am guessing when you say 10:1 or 20:1 that your unit has two ranges? These analog outputs are designed to drive devices like chart/strip recorders or data loggers. I see no reason why you can't run your analog signal out into a comparator circuit using a LM339.

Ron

 

[TheEquineFencer]

10:1-20:1 A/F is the range for the Air/Fuel ratio on the Digital display for the meter on the WBO2 monitor, 0-5VDC is the analog output that relates to the A/F ratio. I'm going to try and post a circuit diagram later when I have time. I just got a call and have to go into work today for a hydraulics problem.

 

[TheEquineFencer]

See what you guys think of this drawing and how it will work?
Solenoids are 1.4 Ohms EACH.

 

[Reloadron]

First, the LM339 has an open collector output so you will need a pull up resistor on that LM339 output. Next, I would use a LM7805 voltage regulator rather than a zener to derive your 5 volt power. Give this a read. If you only need a single comparator you may want to select one of the others in the link. Also note the use of hysteresis. Take into consideration your forward voltage and current on the optocoupler as to a series resistor.

Ron

 

[TheEquineFencer]

I'd like to thank you for the input, no pun intended. I see the drawing with an Non-Inverting Comparator with Hysteresis and with Inverting Comparator with Hysteresis. can you explain what it actually does in "laymen's terms" and which style do I need to use instead of what I have drawn? I think it has something to do with the way the device "recovers" when switching the voltage/current, I'm just not sure when or how to figure or use it.
I should have thought on the LM7805 instead of the Zener, I'll look into what I need to do to replace it. I'll look on Digikey's site to see what they have.

I think it's great that the "little people" can get some help and learn from people like you. THANKS!

Floyd

 

[Reloadron]

Hi Floyd

The attached was done literally on the fly at work today. This should be a start to what you want. Look at ir carefully as I am not even sure it is correct. I know a LM7805 can be had at Radio Shack and I thing as to a MOSFET (if you change your MOSFET choice) they also sell a IRF510 that could be used in the scheme.

I have not tried or simulated the attached circuit so again, I am not sure it will fly. Sort of a busy Mondayt here for me.

What we have is similar to circuit A. Additionally you can play around with the hysteresis resistor. Maybe 1 M Ohm? I used 10 M Ohm in the drawing.

Ron

 

[TheEquineFencer]

Thanks a bunch, I'll round up everything and see how it works in the next day or so, Floyd.

 

[TheEquineFencer]

I was looking on DigiKey for the parts and was going to have them shipped to the house, but I've run into a small problem. When I tried looking up the caps the cheapest 2500uf they list is outrageous. Why type of caps would you use for the planned design? I'm guessing a cheap ceramic for the .1uF caps, I've got a couple of 1000uF radial can type caps here at the house now; the rating is 16V.

 

[Reloadron]

The 1,000 uF caps should work fine. I don't know why they cost so much? I don't get it? 2,200 uF caps at Radio Shack rated for 50 V are 4.29 or so. Use what you have it should work fine.

Ron