| Electronics > Projects, Designs, and Technical Stuff |
| Steering angle/torque sensor tester |
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| omglol:
Hello to all! I would like to build a test device for car steering angle/torque sensor. I'll start with a movie (not mine, of course), because it should make things much clearer to begin with. I would like to make a very similar device, but maybe Arduino based, since this way I can interface simple LCD very easy and fast. However, I have no problems (considerations) with this side (displaying results). I need advice on how to get accurate and reliable readings from the sensor itself. All those sensors work in very similar ways, here is a datasheet for the sensor I will be using: https://www.ttelectronics.com/TTElectronics/media/ProductFiles/Steering%20Sensors/Datasheets/SX-4472.pdf Basically, I need to apply to apply power (GND, VCC) to the sensor and read 5 different output voltages and calculate the values. I need 1 decimal point resolution (.1), with torque (relative angle) ranging from -8.0° to +8.0° and angle ranging from 0.0° to 360.0°. Here are my first questions: 1) How do I know with what voltage should I supply the sensor? Maximum voltage is not specified in the datasheet, but increasing voltage should make easier to get accurate output readings? 2) What kind of ADC should I get in terms of resolution and input voltage? 12-bit resolution should be OK? Using 5V ADC (a part of Arduino) is the simplest way, but what if I want to power sensor with voltages >5V and at the same time avoid using voltage dividers on output? How can I achieve that, is that even a good idea? 3) Datasheet specifies how to filter output voltages just before they reach ADC. Is the manufacturers recommendation OK? Looking at the last page of the datasheet, why did they use 560K pulldown resistor for T1 output, but only 330K for output T2? Why the difference? This will be all for now, many thanks for your help! |
| omglol:
Hmm ... nobody with a hint? :-DMM |
| max_torque:
The sensor datasheet tells us each voltage divider has a resistance of 438 ohms (nominally). For a sensible power dissipation in each divider, you're going to want to keep the excitation voltage low. At 5v, each divider is going to consume around 11 mA and dissipate about 60 mW. If you supply the dividers with the same voltage you use as the ADC reference, then the entire system becomes ratiometric, so you don't need to worry about the stability / variance of your voltage reference. In their suggested schematic, the 10k resistor and 0.22uf capacitor provide a low pass filter, in this case, with a 3bd point at 70Hz, which would suggest you need to sample each channel at around 150 Hz to avoid aliasing. The higher the resolution of your adc, the higher the resolution of your system (for any given level of noise). Something like an arduino with a 10b adc, has 1024 steps, so each of those voltages can be decimated into 1024 descrete steps, so: 1) for the position sensors, that have a FSD over 180 degrees, that a theoretical max resolution of 0.18 degrees 2) for the torque sensors, that have a 10 degree range of 80% of FSD, that's a theoretical max resolution of 0.122 degrees |
| tatersalad:
ill bite, let me start with asking what the purpose is. are you making something out of it or are you trying to troubleshoot a car? what year make and model is the sensor off of? I have a fancy snap on scan tool and it gives me testing hookups so it might point out how to do it. I also have alldata and it is very good with wiring for cars so that might help as well. |
| omglol:
--- Quote from: max_torque on January 31, 2019, 07:54:19 pm ---The sensor datasheet tells us each voltage divider has a resistance of 438 ohms (nominally). For a sensible power dissipation in each divider, you're going to want to keep the excitation voltage low. At 5v, each divider is going to consume around 11 mA and dissipate about 60 mW. If you supply the dividers with the same voltage you use as the ADC reference, then the entire system becomes ratiometric, so you don't need to worry about the stability / variance of your voltage reference. --- End quote --- Nice, thanks. I guess 5V should be fine? Could you tell me (roughly) what would I loose if I choose 3.3V Arduino board (Arduino Due) which has 12-bit resolution ADC? Better resolution ADC, but lower suppy voltage ... consequences? --- Quote ---In their suggested schematic, the 10k resistor and 0.22uf capacitor provide a low pass filter, in this case, with a 3bd point at 70Hz, which would suggest you need to sample each channel at around 150 Hz to avoid aliasing. --- End quote --- I don't really understand this one. Yes, LPF is clear to me, but why would I need sample each channel az 150Hz and what does this mean exactly? I was planning just to read a value from ADC and display in on LCD ... with a simple refresh rate of 3-4 frames per second? --- Quote ---The higher the resolution of your adc, the higher the resolution of your system (for any given level of noise). Something like an arduino with a 10b adc, has 1024 steps, so each of those voltages can be decimated into 1024 descrete steps, so: 1) for the position sensors, that have a FSD over 180 degrees, that a theoretical max resolution of 0.18 degrees 2) for the torque sensors, that have a 10 degree range of 80% of FSD, that's a theoretical max resolution of 0.122 degrees --- End quote --- Yeah, all clear here. I am just considering the most elegant, but accurate enough solution. Since I need to make daughterboard anyway (to put passive components of the low pass filter on it), does it also make sense to put more accurate (12/16-bit) ADCs on it, or do I go with 3.3V Arduino DUE which offers 12-bit ADC out of the box? What is your opinion? Thank you! |
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