| Electronics > Projects, Designs, and Technical Stuff |
| Brain teaser - analog angular position sensor |
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| Turd Furguson:
Hello everyone! Long time reader and subscriber of the EEVblog; first time poster. I’ve been scratching my head trying to recreate an analog angular position sensor from the late 1980s-early 1990s that interfaces with an IC. It is believed to be a 1k dual-gang 360-degree variable resistor opposed by 90 or 180 degrees given the popularity at the time. However, I cannot recreate the expected output readings via potentiometer testing on a breadboard. Through testing and poking around with my oscilloscope I’ve determined the following: Knowns – external direction sensor: * Direction sensor has 4 wires (5v, gnd, sense1, sense2) * When testing wiper readings directly on sense1 & sense2, readings are expected to oscillate sinusoidally; max reading 3.5-4.5v; min 0.5-1.5v. * Expected dead-range within 0-0.5v & 4.5-5v. * Note: I don’t have this part… objective of this mission is trying to recreate it. Schematic: Knowns: mainboard * Sense1 & sense2 wires feed directly into an 8-channel analog multiplexor/switch (IC4 - CH2 & CH3) * From here, signal is routed to an opAmp configured as an integrator to support analog-digital conversion via common pin 3. * Capacitor C9 charges to a value equal to the integral of the input * Channel 1 is selected on IC4 which discharges C9 until TR2 turns off * TR2 Output to IC is a square wave and the discharge time is measured by the microprocessor. * R15, R16 & R17 provide a reference voltage for the integrator and source voltage for the constant rate discharge. Unknowns/thoughts: * Degree separation & expected voltage differences of the two wires by the microprocessor. * Opamp circuit seems to indicate 2.5ish volts input/output based on oscilloscope readings – not sure how 4.5v input is handled, and I don’t see any spikes based on my recreating efforts above. * Recreating voltages of 0.5-4.5v using regular 10k pots on Sense1 & Sense2 generates no output behaviour * This patent seems relevant as I see similar signal patterns in the circuitry, and this also supports rotational angular sensing: https://data.epo.org/publication-server/rest/v1.0/publication-dates/19870225/patents/ep0211477nwa2/document.html Can anyone provide any guidance or direction? This seems like a simple circuit but it’s hurting my brain. |
| duak:
Here's an interesting part: https://www.alps.com/prod/info/E/PDF/Sensor/Position/RDC80/RDC80.pdf It accepts the full 360 deg rotation and has two linear outputs . I was initially thinking of quadraure outputs (sin & cos) like a rotary transformer but it has both a CW and a CCW output which, when I think about it, is easier to use (unless you need sin and cos). |
| Gribo:
Can it be an RVDT aka resolver? |
| Benta:
--- Quote from: Gribo on March 29, 2019, 08:43:27 pm ---Can it be an RVDT aka resolver? --- End quote --- I doubt it. A 360 deg potentiometer is more likely from the circuit shown. |
| Gyro:
A sine/cosine pot? |
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