Electronics > Projects, Designs, and Technical Stuff
Brain teaser - analog angular position sensor
(1/2) > >>
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?
Navigation
Message Index
Next page
There was an error while thanking
Thanking...

Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod