Can you use a micro potentiometer for a TPS Sensor Should be a simple answer.

Thread Starter

born2dive00

Joined Oct 24, 2016
285
I have a question that I think should have a simple solution but I do not know for certain.

I have a on screen display (OSD). The OSD was designed for use with RC electric motors.
The on screen display reads the battery voltage and shows a % or a gauge for the remaining amount of power left in the battery.

I am using this in combination with a gasoline engine, I need to know the position of the throttle on the engine.

What I was thinking of doing was taking the lead from the OSD that monitors the battery and connecting a micro buck boost converter to supply a constant 5v from the main battery.
I was then going to run a + line from the micro buck/boost converter and run it to a potentiometer which would be connected to the arm of the carburetor so when the servo moved the arm it would rotate the pot there by (if I understand this correctly) will increase and decrease the voltage on the power out of the pot. I was going to take the power out put from the pot and run it to the + terminal of the battery lead on the OSD, I would then take the - off the micro buck boost converter and run it to the - on the battery lead of the OSD.

If I am correct in my thinking, the OSD is just monitoring for a voltage increase or decrease. So when the throttle opens it reads X volts100% and when the throttle closes it reads X voltage at 0%. I can program the OSD so that X voltage is 100% and X voltage is 0%

If I am correct in my thinking, the OSD does not have any load on it that that would overload the pot.

Am I correct in my thoughts? would a 50k ohm trimmer pot like this work? https://www.taydaelectronics.com/50k-ohm-trimmer-potentiometer-cermet-1-turn-3362p.html or one like this? https://www.sparkfun.com/products/9806

How would I wire this up, Is how I drew it correct?? Do I need any resistors?
pot as a TPS.png
 
Last edited:

Alec_t

Joined Sep 17, 2013
10,444
The on screen display reads the battery voltage and shows a % or a gauge for the remaining amount of power left in the battery.
I suspect it's more complex than that. Battery voltage alone is not particularly good as a measure of the remaining available energy in a lithium battery. Such gauges often use 'Coulomb counters', which keep track of current.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Hello Alec
Good to see you again my friend, any ideas on how I could make a TPS sensor to work on an OSD??

I suspect it's more complex than that. Battery voltage alone is not particularly good as a measure of the remaining available energy in a lithium battery. Such gauges often use 'Coulomb counters', which keep track of current.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Assuming that the unit does not have a coulomb counter, would the afore mentioned schematic work? Even if the unit had a counter, would there be any problems with using the schematic work or would it cause damage?

I suspect it's more complex than that. Battery voltage alone is not particularly good as a measure of the remaining available energy in a lithium battery. Such gauges often use 'Coulomb counters', which keep track of current.
 

Alec_t

Joined Sep 17, 2013
10,444
I can program the OSD so that X voltage is 100% and X voltage is 0%
If you are able to program the display purely as a voltmeter, then if a regulated (constant) voltage is applied across the potentiometer (i.e between the terminals shown as Vcc and ground, rather than connected as shown) the voltage between the wiper and ground would be a measure of the wiper position.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Hello Crutschow good to see you again also.
The purpose of monitoring the engine position is 2 fold, as this will be operated remotely, I can see the throttle position in relation to the rpm so this will allow me to calculate fuel consumption as well as verify that the engine is running and not stalled. Also Crutschow the engine is very small 25cc, and I am adding a aftermarket EFI to it, but the TPS sensor that comes with it is too DAMN BIG! hence why I am asking about using a micro pot with a buck boost converter.

What is the purpose of monitoring the engine throttle position?
 
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Thread Starter

born2dive00

Joined Oct 24, 2016
285
@ Alec like this ?? Below is the snap shot of the configuration screen, The battery can be set to show volts, current, MAH used MAH available, and wattage. It can by default show the voltage of a battery, hence the reason I was thinking of using a pot as a TPS sensor.
pot as a TPS.png
If you are able to program the display purely as a voltmeter, then if a regulated (constant) voltage is applied across the potentiometer (i.e between the terminals shown as Vcc and ground, rather than connected as shown) the voltage between the wiper and ground would be a measure of the wiper position. The values in this case that they wan you to fill in is volts.
bat tps.png
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Alec or Crutschow
A friend of mine told me to use this but I am un sure how it will work as I need a rotational movement to get something to create a dynamic resistance value. Is he meaning to use this instead of a buck boost converter then connecting this with the pot???TPS.PNG
 
This
guy did pretty well checking the sensor. Note, he says at idle, the sensor does not read zero.

It should be nothing more than a potentiometer attached to a 5V reference.

Automotive sensors typically don't output 0V and they are what's called ratiometric. The A/D converter that measures the output is relative to the actual 5V voltage at the time of measurement. It could be 4.8 or 5.1 V at the time of measurement. In all cases 4.8 or 5.8 is read as 100%.
When starting the vehicle, the 5V supply could drop too. You also don't need to be concerned about the accuracy and temperature sependence of the reference voltage.

Using 1-5V also helps remove quantization errors. +-1 bit at 0V means your readings are varying +-100%. 1 bit at 1V is considerably less.
Assuming, say a 12 bit positive values only A/D converter. 2^11 full scale number of counts.
 

Reloadron

Joined Jan 15, 2015
4,582
Alec or Crutschow
A friend of mine told me to use this but I am un sure how it will work as I need a rotational movement to get something to create a dynamic resistance value. Is he meaning to use this instead of a buck boost converter then connecting this with the pot???View attachment 155856
Yeah, that is what he means but you want to look at the video which KISS was kind enough to post. The L4931-3.3 is a low dropout voltage regulator popular in some automotive applications. You do not get 5 volts out. This is the data sheet for the L4931 Very low drop voltage regulators with inhibit. Using a 5 Volt version would likely be a better choice. You apply the 5 volts to one leg of the TPS and ground to the other leg. The wiper is the TPS output which is passed on to your A/D converter. Note the typical voltages shown in the video. The idle was about 0.95 volt so that becomes 0.0% when you scale it and the wide open throttle voltage becomes 100% when you scale it. This is just a matter of how you scale your display.

Ron
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Hello Kiss Thank you so much for that video it really did a good job at clarifying the voltages. and how it works.

] guy did pretty well checking the sensor. Note, he says at idle, the sensor does not read zero.

It should be nothing more than a potentiometer attached to a 5V reference.

Automotive sensors typically don't output 0V and they are what's called ratiometric. The A/D converter that measures the output is relative to the actual 5V voltage at the time of measurement. It could be 4.8 or 5.1 V at the time of measurement. In all cases 4.8 or 5.8 is read as 100%.
When starting the vehicle, the 5V supply could drop too. You also don't need to be concerned about the accuracy and temperature sependence of the reference voltage.

Using 1-5V also helps remove quantization errors. +-1 bit at 0V means your readings are varying +-100%. 1 bit at 1V is considerably less.
Assuming, say a 12 bit positive values only A/D converter. 2^11 full scale number of counts.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
So now my question still stands. If I use this L4931-5.0 https://www.adafruit.com/product/2236 it says that I only need 5.4v to get a 5 v signal out, so I if i take my 3S lipo which supply between 9-12.6VDC to the system. So if I take a tap and run it to the L4931 -5.0 This should replace the need for the buck boost converter to the pot correct?

So if my batteries are supplying greater than 5.4vDC this little unit should give me 5VDC Now what values do I have to use for the resistors if using a 12v power supply. Originally this schematic was for a 5v system with a 3.3v output. TPS.PNG
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
I am having a headache finding a 1 turn micro potentiometer. all small the ones I am finding are either 10 turn trim pots or big a$$ 1 turn metal pots.

Using the L4931-5.0 on a 9-12.6v system, can a make a suggestion for a correctly sized micro pot with 1turn

Thank you.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
I would really like a round one like this a 1/4" - 3/8". I can not find one that has only 1 turn. This way I can simply insert it in a tube that buts up against the barrel of the carburetor, and insert the end of the tube on to the body of the carburetor. then just run the wire out the tube. The one you posted Crutschow would work but it is not preferred.
770259.jpg
 

Reloadron

Joined Jan 15, 2015
4,582
Rather than try to modify a pot like those you have listed a simple trip to an automotive junk yard should yield dozens of TPS units. Just find one easily modified for your application. Also places like Amazon list dozens of actual TPS sensors with many less than $12 USD in cost. Another solution is to use a linear motion potentiometer similar to these. The actual value of the pot is not all that critical. Any 5K or 10K pot should do fine. The lower the value of the pot the greater the current through the pot if you are current conscious for battery life. Do you know the input resistance of your A/D converter (your display)? It is likely high so again any 5K or 10K pot should do fine.
You may also want to keep in mind that a 1 Turn pot typically is not a 360 degree rotation, check an actual manufacturers data sheet as most are 260 / 270 degree rotation.

Ron
 
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