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# Engine Temperature using an AD590 on the Oil Pressure Wire to the engine

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#### crutschow

##### Well-Known Member
Maybe one of these TMP-36 would be easier to work with also less expensive TMP36 Datasheet
How would it be easier to work with?
They provide a voltage output which would require a different circuit, which would need to isolate the output voltage from the oil switch operation.
Also that low voltage output might be more prone to noise pickup.

I would stick with a current output sensor.

#### Danwvw

##### Active Member
Later EDIT: "Updated" Yeah, Hun! Well, OK. I am rapping my brain around this as I type. So, are your saying to Modify the HP circuit to run in the car and run it with this TMP-36 chip would be more work? What are you saying? Yeah will see this 590 Idea through if you help. Just ordered some 731' and 358's!

Something of interest Back in the 80's Tested one of these HP Transducer circuit boards for Gain VS Frequency all remember is they were Non linear below 10 HZ with DC gains somewhat less than the AC

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#### Danwvw

##### Active Member
Actually What I need is them configured for Temperature on a break out board But I can build the first circuit we came up with them.

#### Danwvw

Guess I will use this post which is before your post Mr. "crutschow" Thanks for the heads up on the LM358 I have some TSH-82 on order also that I was planning on using on my Voltage Regulator on my other electro-tech thread, Kind of expensive though. $12 each. One thing I could do is since I have the HP LM358 Temperature interface boards already is to use one on the 6-30 Volt Boost Converters I just happen to have a few off then it would cover the full range of Ambient Temperatures Below Zero too. Thanks for all your help. Last edited: #### crutschow ##### Well-Known Member Most Helpful Member The LM358 will not pull the output down to only 100-200mV above ground when used with a single supply. That's why I used a CMOS op amp in my circuit which will go close to 0V. #### Danwvw ##### Active Member Everyone Feel Free to help me figure out how to use the circuit with an AD590 Probe: #### crutschow ##### Well-Known Member Most Helpful Member How are you going to generate the +/- 15V supplies? #### Visitor ##### Well-Known Member I looked at this a while back and thought - the perfect place for a DS18B20 1-wire probe. They are available as a sealed probe with a meter of cable for less than 10 bucks and pre-calibrated independent of supply voltage. I got some time to noodle about with this this morning, and I believe it offers a pretty simple solution. The schematic is shown below. The bulb and pressure switch are the stock parts. The DS18B20 operates off 5.5 volts maximum. So first, we add a zener diode prior to the bulb to essentially remove it from the circuit except when the pressure switch is closed (indicating low pressure). R1 (paralleling the bulb and zener) and R2 form a voltage divider to supply 5 volts to the DS18B20 (operating off of parasitic power - Vdd not connected) with the battery voltage at 14.7 volts. The 5 volt zener on the DS18B20 data line protects it from over-voltage, and I believe some low-value series resistor will be tolerated in the data lines to the DS18B20 and the micro. A micro with a small LCD display in the car will display temperature, accurate to better than 0.5°C. This could be an Arduino and sample code is available to display a temperature on an LCD display. When the pressure switch closes, the 10 volt zener will have 12+ volts across it, so it will conduct, turning on the existing bulb. The micro input and DS18B20 data line will be at near-zero volts when this happens, so they shouldn't be damaged. Feel free to pick this idea apart #### crutschow ##### Well-Known Member Most Helpful Member Feel free to pick this idea apart Looks okay, if you understand coding and have the ability and equipment to program a micro. It's not something I would suggest for someone with no coding or micro experience unless they are willing to take the time and effort to learn that. #### Visitor ##### Well-Known Member Looks okay, if you understand coding and have the ability and equipment to program a micro. It's not something I would suggest for someone with no coding or micro experience unless they are willing to take the time and effort to learn that. Literally, you can find example code to do exactly this all over the internet.$15 – $20 should get everything needed to do this. #### crutschow ##### Well-Known Member Most Helpful Member Literally, you can find example code to do exactly this all over the internet.$15 – $20 should get everything needed to do this. That's not my point. You still have to learn how micros work and understand the code. If you don't know that, it's like trying to build a circuit with no understanding of electronics. #### Danwvw ##### Active Member Yes it might be worth it and sure a lot of fun, I have always been on the B string when it comes to anyone trusting my programing. I took classes in it once and have a lot of experience with it as a user of the programs others have written but as far as doing this that way I think for this thread I will stick with Analog because I want to perfect the Analog temperature readout first. The HP interface board could be left pretty much alone I have an off the shelf already built Boost Converters that might work. Just checked my Boost Converters and the problem is ground is common between Input and Output! So Yeah! A Problem! Last edited: #### Visitor ##### Well-Known Member Well, if the analog method doesn't work out, the code required is literally available as examples from many sources. Here's one example, which would cost less than$20 for Arduino, oLed display and sensor. The Arduino IDE is free, and the "programmer" is a USB cable.

Good luck however you do it. Taking advance of a single wire is a great idea.

#### Danwvw

##### Active Member
Thanks "Visitor"

As far as Analog goes, I guess it could work, If I
mirrored the -6.3 volt Supply with a +6.3 volt Supply on the HP board to run the Display with It would need a little balancing but it has resistors for that and Signal Output B could tie directly to Output 1 Common and display ground but not the car ground.

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