After helping a fellow racer at the track diagnose an issue with his ESC and motor and having dealt with a similar issue with a damaged sensor cable, I decided to build a tool to help. I wanted something that could test each of the 3 hall effect sensors in the motor without having to take the motor out, just unplugging the sensor cable. I also wanted something that would test the sensor cable itself.

You plug the motor into the motor connector on the board and turn the rotor. The individual phases light up similar to the SkyRC motor tool.

You plug the sensor cable into both connectors on the board and if the cable is good, it lights up all 3 phases plus the Power/Ground LED. It doesn't test the temp pin, but I wasn't really concerned about that.

It will run off any power source between 6-30V. I originally was thinking of using a small 2s lipo, but that would require a BMS. So I just used a 9v battery.

Here's the schematic if you want to build your own. I have a couple of boards left over from building a couple of these for guys at the track. PM me if you're interested in buying one.

I did end up using a higher resistor for the power LED since that blue LED was blinding.

SensorMate schematic





Testing the cable

Testing the motor

How you connected the LED's for a motor sensor test is not perfect. Most sensors work with a transistor switching to the ground and an internal pull up of 10k and some even no internal pull up. I suggest to use a simple buffer like an ULN2003 or something like a 74hc04, 74hc06 or 74hc07 with on the input a pull up in the range of 10k~22k

That's probably why it didn't work on one of my motors. It's output voltage was very low when triggered. Didn't think about a pullup resistor. I'm still learning.

What would you use to control the transistors? A 555 timer?

I would wire the sensor LEDs to the 5V rail, use a 470ohm resistor on them to limit the current less than 10mA (worse case red led with 1.8V forward voltage should be around 7mA). The open collector output of hall sensor can sink some current, that is the idea, but they can't sink a lot.

I think what Roelof is suggesting is using an invertor as a buffer. When the output goes low the inverter will source to the open collector. and then output a 1, which will be pulled low by the LED and resistor. Again, these inverters are not high current devices so I would use a 470ohm resistor instead of the 220ohm you are using since two LEDs can be on at a time.

No need for a timer, this system isn't going going to have logic races, so no need to clock the inputs.

I have seen some specs of these sensors and yes, they are not specified for normal LED currents of 15 to 20mA, some max 10 and some even not more than 2 up to 5mA, that is why you better could use some buffer. The idea of Trilerian will work also and only need some rework and slight mods to your PCB.

Here's an updated schematic. I breadboard tested to make sure I had everything correct. Now it works with those couple of motors that must not have built in pull up resistors in their hall effect sensors. I appreciate your help.

Now I'm wondering if I should make my cable testing function better with a 555 and CD4017 to cycle through the LEDs. Wanted to try and keep this as simple as possible. Scope creep.

I'd like one once you get it figured out.

Since I'm incorporating the changes the guys here suggested, I'm also planning on changing how the sensor cable test works. I'm just waiting for some parts so I can breadboard these changes before ordering new boards from abroad.

I decided I might as well incorporate a better wire tester, since I found one of my sensor wires had a short between 2 of the phases, which didn't show up when testing. Now it cycles turning off 1 phase LED every second.

My latest schematic with this new wire testing is updated in the first post.

Thank you guys for the help.

The 4017 is able to power LED's, why not making it a 6 counter and another connector with 6 LED's. This is how most simple ethernet cable testers also work.