# how to use transistor to increase resistance

#### MrChips

Joined Oct 2, 2009
26,103
I suggest avoiding anything that may disrupt the MCU, probably the most expensive component in the whole vehicle.
You mean not making connection to the ECU which I agree. Hence we are discussing making use of the unused thermistor in the sensor plug.

#### MisterBill2

Joined Jan 23, 2018
11,880
You mean not making connection to the ECU which I agree. Hence we are discussing making use of the unused thermistor in the sensor plug.
That is exactly what I am suggesting! If it will work then that will be the very best option. And adding a series resistor is a simple solution, if it can be made to work adequately.

#### MrChips

Joined Oct 2, 2009
26,103
That is exactly what I am suggesting! If it will work then that will be the very best option. And adding a series resistor is a simple solution, if it can be made to work adequately.
I have done the modelling on the computer. No series or parallel combination gives any hope of a reasonable result.
The only solution I have to offer is a mathematical transformation from the input signal to degrees temperature output or at least to a resistive output to mimic the required input of the off-the-shelf digital thermometer. From the data submitted the W1209 digital thermometer appears to be using a 10kΩ thermistor.

If we know how the digital thermometer transforms resistance to readout then there are other solutions.

We don't know if the digital thermometer is measuring current, voltage, pulse duration or pulse frequency. Examining the input connection via an oscilloscope would provide us with some clues.

#### MisterBill2

Joined Jan 23, 2018
11,880
Examining the voltage from each sensor terminal to the supply negative will tell us a lot, and is much more likely to be possible.
And as I saw those curves, blue and yellow, simply adding a series resistor will bring the curves closer to each other.

#### Alec_t

Joined Sep 17, 2013
12,810
We don't know if the digital thermometer is measuring current, voltage, pulse duration or pulse frequency. Examining the input connection via an oscilloscope would provide us with some clues.
Agreed. Even measuring the voltages as I suggested in post #51 would be a help.

#### MisterBill2

Joined Jan 23, 2018
11,880
Agreed. Even measuring the voltages as I suggested in post #51 would be a help.
And as I repeated in post #64, including the reference connection.

#### saeidbb

Joined Jan 21, 2022
25
I have done the modelling on the computer. No series or parallel combination gives any hope of a reasonable result.
The only solution I have to offer is a mathematical transformation from the input signal to degrees temperature output or at least to a resistive output to mimic the required input of the off-the-shelf digital thermometer. From the data submitted the W1209 digital thermometer appears to be using a 10kΩ thermistor.

If we know how the digital thermometer transforms resistance to readout then there are other solutions.

We don't know if the digital thermometer is measuring current, voltage, pulse duration or pulse frequency. Examining the input connection via an oscilloscope would provide us with some clues.
I do not have much electronics in the field and everything I know is related to my field of study, namely physics.
I have a multimeter from electronics that measures voltage, current and resistance, and that may not be accurate. And I do not have access to an oscilloscope.

#### saeidbb

Joined Jan 21, 2022
25
Agreed. Even measuring the voltages as I suggested in post #51 would be a help.
[/QUOTE

Unfortunately in post#51 I did not know exactly what I should measure. If you explain more and say more accurately, I can measure what you want.

#### MisterBill2

Joined Jan 23, 2018
11,880
With the digital sensor connected to the supplied sensor digital display and a power supply, measure the voltage from each sensor terminal to the 1 volt source negative (common) then change the temperature of the sensor probe to some warmer value, preferred at least 10 to 20 degrees warmer. That should be adequate for what I am thinking about.

#### MrChips

Joined Oct 2, 2009
26,103
I do not have much electronics in the field and everything I know is related to my field of study, namely physics.
I have a multimeter from electronics that measures voltage, current and resistance, and that may not be accurate. And I do not have access to an oscilloscope.
That's a great place to start! My background is in math and physics. So that is an asset.
A DMM will do. Does it have frequency measurement option?

#### Alec_t

Joined Sep 17, 2013
12,810
saeidbb said:
Unfortunately in post#51 I did not know exactly what I should measure. If you explain more and say more accurately, I can measure what you want.
Fleshing out what I intended, and what MisterBill2 is saying in post #69, this is what the test set-up should look like :-

The 1209 unit should have its +12V supply connected for the test.

Last edited:

#### MisterBill2

Joined Jan 23, 2018
11,880
Measurements of the voltage from bot A and B, and at 3different temperatures: ambient, "hot" and almost boiling. if that is possible We do not need to know the temperature value, ambient, hot, and "very hot" are adequate descriptions..

#### Alec_t

Joined Sep 17, 2013
12,810
Out of interest, in the pic above (which I assume matches the 1209 that the TS has) I'm guessing IC2 is a 5V voltage regulator. Also, the 10k resistor R2 could connect between ground and the thermistor to make a voltage divider.

#### MisterBill2

Joined Jan 23, 2018
11,880
Out of interest, in the pic above (which I assume matches the 1209 that the TS has) I'm guessing IC2 is a 5V voltage regulator. Also, the 10k resistor R2 could connect between ground and the thermistor to make a voltage divider.
Possibly so, but I am not going to speculate as it would serve no purpose. The requested voltage readings wi provide the information that I require..