Increasing 0.15v to >1v?

Hi Folks

I'm quite a novice when it comes to circuits.. So hopefully someone could please help with the following problem I'm facing..

I've got a vehicle tracking system that logs when a vehicle door is unlocked. It is negative triggered and as such when the door is locked a voltage of 0.14-0.16V passes over the central locking unlock wire. When I unlock it drops to 0.

The issue is my tracking devices only pick up the door as locked if the voltage across the central locking wire is >1V and as such interperets the 0.14-0.16V as unlocked, even though it is not.

I have tapped in to the door wire and I'm running off a seperate feed, I also have a 12V DC supply if required. The input for my tracker can take up to 45V, 500mA max. Could someone kindly recommend a work around to get me from 0.14-0.16V input to >1V output while still allowing for the voltage to drop back to 0 when unlocked?

Thanks in advance
Steve

Use OpAmp rail to rail such as OPA340 to amplify the input - use non inverting schematic with amplification. You need ~20x amplification to get 0.14V to 2.8V

Check the TIP#15 level shifter in page 46 (4-16), it uses a comparator
https://ww1.microchip.com/downloads/en/DeviceDoc/01146B.pdf

Alex

It sounds really unlikely, that such a low voltage is used for signaling purposes in automotive electronics.

Be careful about noise, mobile phones etc giving you false signals at these low voltages...

Hi folks

Thank you for your replies.

I've started looking at creating the non-inverting opamp circuit. with the following circuit:



Will using the following resistors and powering from a 12v DC supply work with the LM741 opamp? **broken link removed**

Vin = ~0.15V
Rf = 1000 ohm
Rg = 100 ohm
Vout = 0.15 * ((1000 / 100) + 1) = 1.65V

Many Thanks

---------- Post added at 16:17 ---------- Previous post was at 15:15 ----------

@FvM

I've double checked the voltage across the wire on 2 ford transits now and it has ~0.15V when the vehicle is locked and drops to 0 when unlocked.

Thanks

Why did you choose 741?
It is a vary basic old opamp and I think it doesn't work with single supply.

Alex

Hi Alex

Thanks for your reply. The main reason I used the 741 was the following blog.

How to Use an Operational Amplifier | eHow.com

It uses the 741 in an identical scenario to mine.

However lets say If I power the 741 V+ to a 9v battery and V- to its negative terminal the output on my pin 6 is 9V is this correct? :|

The issue I am having is that even although I have wired up following the blog I still get the input supply voltage as the out?

And I'm using the AA battery as a test input with a common ground

I've attached a photo of my breadboard. Using a hard disk 12VDC supply

I'm not sure as to why even though if only the V+ & V- of the opamp are hooked up to my supply the voltage on pin 6 is 12v?