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

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Reloadon automotive TPS sensors are way too big for a 25cc engine. but thank you, also I can not use linear as I need a rotational movement.


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
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Hello Alec
Thank you for confirming this.

Adjusting the 3.3v schematic to 5 volts, what value should I replace the resistor with for a 5v, also what ohm pot should I use with the 5v version??

Do I need to change out the caps to a different size?
So as a recap using 3s lipo, 9-12.8v, using the L4931 -5.0 and the 1/4" pot what size resistor and caps and pot should I use??


Only if you choose the 5V version. In your pic it's a 3.3V version.
 

Alec_t

Joined Sep 17, 2013
11,501
I'd use anything in the 2k-5k range for the pot. As for the caps, use the values suggested in the application circuit in the IC's datasheet.
 

Reloadron

Joined Jan 15, 2015
5,600
Reloadon automotive TPS sensors are way too big for a 25cc engine. but thank you, also I can not use linear as I need a rotational movement.
Yeah, I was sort of thinking converting rotational to linear, much like what you see attached to a servo motor using a simple linkage. Thus a simple linear pot could be used.
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
The only 2 problems with that in my application is 1 limited space, and 2 how to connect a linkage from a servo to a push wire push wire to the pot wire from the pot wire back to the push wire all the while maintaining the body of the pot stationary. I like the ingunity and your thought process, but it just wont work for my application.

Yeah, I was sort of thinking converting rotational to linear, much like what you see attached to a servo motor using a simple linkage. Thus a simple linear pot could be used.
 

Reloadron

Joined Jan 15, 2015
5,600
No problem, it was just a thought from my past. :) Working with the restraints of space can be difficult. Then just run with a 5K or 10K pot like you have in mind. That should work fine. Keep in mind what I mentioned earlier that a 1 turn pot does not mean 360 degree of rotation, they are generally about 260 degrees of rotation. That should not matter for a TPS.

Ron
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Hello guys I thank you all for your help with this matter I have a few more questions.
This is a updated schematic that was given to me by a good friend who has worked with this OSD in the past. It will take the voltage from the main line and drop it to 5vdc. He says due to how the OSD is setup this is the correct schematic.

Now I was told to use a linearithmic pot rather than a logarithmic.
I would like to use these 5k Ohm pots but I do not know if they are linear, it says they are linear taper, is this the same thing??
https://www.ebay.com/itm/Bourns-3329H-1-502-VP-82PR5K-1-4-Inch-Round-Cermet-Potentiometer-5K-Ohms-30-pcs/122307935783?hash=item1c7a1efe27:g:S4QAAOSw9GhYdm57

Alternatively, I have access to these 2k Ohm Bourns pot https://www.ebay.com/itm/Bourns-3329H-1-202-VP-82PR2K-1-4-Inch-Round-Cermet-Potentiometer-2K-Ohms-10-pcs/122307935700?hash=item1c7a1efdd4:g:2oMAAOSw44BYdm50

Seeing that a pot has 270 degrees rotation, and mini carburetor that this is going on has only about 90 degrees of rotation on the barrel means when I put this in the tube with a blade insert from the barrel of the carb to the slot on the pot, I get only 90 degrees of rotation.

Or better said the closed point of the carb / the0 point of the pot for me would be @ 90 degrees, 50% throttle position would be at 135 degrees, and the WOT / 100% position would be at 180 degrees.

Now Ideally at 0/closed position I would have .95v, 50% 2.5v and100% 5v all within a 90 degree sweep.

As the OSD does not allow a curve to be programed, only linear program. I believe that an inverted taper pot will not work. So using a linear pot, how can I get closer to these voltages?

Is there such thing as a 90 degree pot?



TPS.PNG
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Ok using 5 volts on the pot
Seeing that most pots are 270 degree rotation, this means that the pot has to move 54 degrees per volt.
So if my starting position is 90 degrees the starting voltage is 1.66v
by the time carburetor barrel swings 90 degrees from the starting position at 90 degrees, to the final position at 180 degrees, the voltage go from 1.66v to 3.33v

Now ideally I want a swing voltage 3.68v or better said starting voltage at .95v to 4.63v
So with a standard 5v power supply, on a 270 degree rotation, with a linear taper, using a movement of only 90 degrees of rotation, How can I get the voltage within the .95v to 4.63v without increasing tie input voltage?

According to my math I would need to use 11v in with the 270 degree pot. The problem is 11v would be too high with out using a buck boost converter, when the voltage of the battery voltage drops down to 9v.

Any Idea how to make this work?
Some folks said that I should use a 5k pot, but would using a lower ohm pot work better say a 500ohm to the target range??
 
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Reloadron

Joined Jan 15, 2015
5,600
I suggest you just start with the pot you get, interface it, and then see what you get. It looks like from your earlier screen shot that your OSD software solution allows you to scale what you get to what you want which is 0 to 100% on your display. You can use a 0 to 5K pot, a 0 to 10K pot the output will be the same. The only change will be the current through the pot.

For example you apply 5.0 V across the pot with a 5K pot the current through the pot will be 5 V / 5,000 Ohms = 0.001 Amp or 1.0 mA. Using a 10K pot it will be 5 V / 10,000 Ohms = 0.00050 Amp or 0.5 mA. The wiper voltage out will be the same about 0.0 to about 5.0 Volts. All assuming your OSD (A/D) has a very high input impedance which most do.

Your pot will have let's say "X" amount of rotational travel and for the total travel the pot will output 0.0 to 5.0 volts (approximately). Each 1/4th travel will be equal to about 1.25 volts. So here is what you have:

Single-turn pot
Single rotation of approximately 270 degrees or 3/4 of a full turn

Note the use of "approximately" as basic inexpensive potentiometers are not quite precision instruments.

Anyway it looks like your OSD software (A/D Converter) allows you to scale your inputs which is what you want to get your 0 to 100% of throttle position.

Ron
 
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Thread Starter

born2dive00

Joined Oct 24, 2016
285
Hello reload
Thank you for that clarification. I was thinking back to when I build my bench top power supply I had one pot for course adjustment which had high ohms and one pot for fine adjustment, the large pot was super sensitive to even the most minor touch and when I put a small pot on the fine adjustment I got very low adjustment on the voltage when I put a larger pot on I got larger swings this is why I asked about using a smaller pot. But this makes sense now with what you are saying, and it was a different setup as I said.

I will give it a shot with the 5k pot and see what happens, probally the best thing to do is to measure the Ohm resistance on the camera and match that??

I hope that the OSD is sensitive enough to measure accurately the 1.66v shift over 90 degrees. That is my concern is if the voltage shift is too small for accurate readings say at .05v intervals.

Thank you for all your help I will give it a shot after we get moved and unpacked.

I suggest you just start with the pot you get, interface it, and then see what you get. It looks like from your earlier screen shot that your OSD software solution allows you to scale what you get to what you want which is 0 to 100% on your display. You can use a 0 to 5K pot, a 0 to 10K pot the output will be the same. The only change will be the current through the pot.

For example you apply 5.0 V across the pot with a 5K pot the current through the pot will be 5 V / 5,000 Ohms = 0.001 Amp or 1.0 mA. Using a 10K pot it will be 5 V / 10,000 Ohms = 0.00050 Amp or 0.5 mA. The wiper voltage out will be the same about 0.0 to about 5.0 Volts. All assuming your OSD (A/D) has a very high input impedance which most do.

Your pot will have let's say "X" amount of rotational travel and for the total travel the pot will output 0.0 to 5.0 volts (approximately). Each 1/4th travel will be equal to about 1.25 volts. So here is what you have:

Single-turn pot
Single rotation of approximately 270 degrees or 3/4 of a full turn

Note the use of "approximately" as basic inexpensive potentiometers are not quite precision instruments.

Anyway it looks like your OSD software (A/D Converter) allows you to scale your inputs which is what you want to get your 0 to 100% of throttle position.

Ron
 

Reloadron

Joined Jan 15, 2015
5,600
Something else you can do is place a resistor above and below your pot. Just as a quick example, using a simple ratio, if I place a 5K resistor between 5 V and the upper leg of the pot and a 5K between the lower leg and ground my pot range would be about 1.66 V to 3.34 V. The resistances can be changed to get a lower limit above zero and an upper limit below 5.0 Volts. For what it's worth you could use a few pots and adjust to whatever you want for the TPS range.

The overall accuracy and resolution of your display will be a function of your OSD A/D converter. For example a 12 bit A/D conversion will yield 2,048 bits. So if the A/D has a 5 volt reference then you get 0 V = ) Bits and 5.0 Volts = 2,048 bits. Therefore 5 Volts / 1,024 bits = 4.8 mV per step change. That is the resolution.

Ron
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
Reload I think I am getting you but I am not sure (theory is not my strong point)

What I need ideally is a voltage of
.95v when the pot wiper is at 90 degrees,
and 4.66v when the pot is at 180 degrees
with 5 volts applied to the pot.

I follow where you are saying to put resistors, BUT by placing the 5k resistors will it adjust the voltage to where I need it?

I am sorry as I can not test this at the moment as all my gear is packed as we are moving to our next assignment in Cairo.

If what you are saying is as I described, could you let me know exactly what size resistors I would need please.

Based on using just applied voltage I found that I needed to apply 11.1v to the pot to get the numbers stated above.

If we can use resistors and applying only 5v to a 5kohm pot, to get a voltage change of 3.68v over a 90 degree swing that would be great!

Please let me know.

Something else you can do is place a resistor above and below your pot. Just as a quick example, using a simple ratio, if I place a 5K resistor between 5 V and the upper leg of the pot and a 5K between the lower leg and ground my pot range would be about 1.66 V to 3.34 V. The resistances can be changed to get a lower limit above zero and an upper limit below 5.0 Volts. For what it's worth you could use a few pots and adjust to whatever you want for the TPS range.

The overall accuracy and resolution of your display will be a function of your OSD A/D converter. For example a 12 bit A/D conversion will yield 2,048 bits. So if the A/D has a 5 volt reference then you get 0 V = ) Bits and 5.0 Volts = 2,048 bits. Therefore 5 Volts / 1,024 bits = 4.8 mV per step change. That is the resolution.

Ron
 

Reloadron

Joined Jan 15, 2015
5,600
Following some thought here is the problem you are going to have with your numbers.
What I need ideally is a voltage of
.95v when the pot wiper is at 90 degrees,
and 4.66v when the pot is at 180 degrees
with 5 volts applied to the pot.
So we have a pot with a total of 270 degrees of rotation. The throttle body going from closed to WOT (Wide Open Throttle) has a span of 90 degrees of travel or 1/3 of the pot 270 degrees. With 5 Volts applied any given 90 degrees of travel of the pot will give a voltage span of 1/3 of 5.0 or 1.666 volts. That span being as good as it gets. You can for example mechanically adjust your pot so it starts at 1/3 rotation which is 90 degrees which would be 1.666 volts out and at WOT the pot would be at about 3.332 volts. So 0.0% = 1.666 Volts and 100% would be 3.332 volts. The span is always going to be 1.666 volts or 1/3 of the 5 volt reference. Adding resistors in series with the pot will only decrease that span.

You can increase the voltage to for example 10 volts which will just double the numbers so you would have a span of 3.333 Volts for each 90 degrees of rotation. Keep in mind that throttle position sensors are designed for what they do in that most throttle bodies only have about 90 degrees of rotation between 0% and WOT of 100% so unlike a pot with 270 degrees of rotation they only have about 90 degrees rotation between 0 and full scale output.

The question is also what is the upper voltage limit for your A/D converter? You do not want to work with any voltage which exceeds the max A/D input. If something goes wrong, like an open ground for example, you can over voltage the OSD A/D. Also, I don't know what the A/D is, as in bit count? That will tell you how well it will resolve the incoming voltage and how much is enough.

Ron
 

Thread Starter

born2dive00

Joined Oct 24, 2016
285
The OSD can handle up to 12v. The problem is the ECU, the ECU is looking for .5v to 5v

I figured if I applied 11.1v, it would get me Damn close to the desired out puts of .5 to 5v BUT if something failed and the voltage spiked good bye ECU, and the second issue is maintaining a voltage of 11.1 even if the battery drops to 9v. Hence the thought of using a buck boost converter


Following some thought here is the problem you are going to have with your numbers.

So we have a pot with a total of 270 degrees of rotation. The throttle body going from closed to WOT (Wide Open Throttle) has a span of 90 degrees of travel or 1/3 of the pot 270 degrees. With 5 Volts applied any given 90 degrees of travel of the pot will give a voltage span of 1/3 of 5.0 or 1.666 volts. That span being as good as it gets. You can for example mechanically adjust your pot so it starts at 1/3 rotation which is 90 degrees which would be 1.666 volts out and at WOT the pot would be at about 3.332 volts. So 0.0% = 1.666 Volts and 100% would be 3.332 volts. The span is always going to be 1.666 volts or 1/3 of the 5 volt reference. Adding resistors in series with the pot will only decrease that span.

You can increase the voltage to for example 10 volts which will just double the numbers so you would have a span of 3.333 Volts for each 90 degrees of rotation. Keep in mind that throttle position sensors are designed for what they do in that most throttle bodies only have about 90 degrees of rotation between 0% and WOT of 100% so unlike a pot with 270 degrees of rotation they only have about 90 degrees rotation between 0 and full scale output.

The question is also what is the upper voltage limit for your A/D converter? You do not want to work with any voltage which exceeds the max A/D input. If something goes wrong, like an open ground for example, you can over voltage the OSD A/D. Also, I don't know what the A/D is, as in bit count? That will tell you how well it will resolve the incoming voltage and how much is enough.

Ron
 

MrSoftware

Joined Oct 29, 2013
1,860
Something to keep in mind; think about how much your throttle will move over time. If your application requires varying throttle opening (like a car, RC toy, weed whacker, motorcycle, etc..) then over time the throttle will move a lot. Like a lot a lot. A real TPS is designed to operate this way and will last a long time. Many standard small POTs are only intended to be moved a few times and probably won't hold up under the same conditions that a real TPS will.
 
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