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Can I use 3rd-party temperature sensors with FrSky smart port sensor?

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Allan Bennett21/06/2017 21:43:00
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In my scale helis I have installed these 10k thermistors in my motor and ESCs to log temperatures on my Eagle Tree data logger.

Now that I've converted the models to Taranis/FrSky I might as well get real-time temperature alerts, and it would save a lot of hassle if the FrSky smart port sensor could work with these thermistors instead of the supplied sensors, especially as the supplied ones, being loops, do not lend themselves to embedding in the motor windings.

Does anyone know if I can do this and get meaningful readings please?

Frank Skilbeck22/06/2017 16:14:43
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Allan, have you seen the OpenXsensor projects, using Arduino boards to talk to the smart port, you'd have to configure it with your thermistors but you should be able to get it to work.

I've built a few Varios for use with the Multiplex M Link system and they work well.

Allan Bennett22/06/2017 20:25:50
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I haven't seen the OpenXsensor projects, and I might be interested once I find my way around the site that you linked. I've used PICAXE chips for projects, but not Arduino. I wonder if PICAXE could talk to the smart port?

But, to be realistic, if the sensor can't use my existing thermistors, it's still probably simpler to find a way of getting the supplied FrSky thermistors (or whatever their sensors are) to make good contact with my motor windings -- the ESC shouldn't be a problem.

Allan Bennett26/06/2017 20:15:12
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I emailed the question to T9, and they've replied that I can't substitute for the supplied sensors sad

Mike Blandford26/06/2017 22:43:16
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I think you will find the FrSky thermistors are 100K. What you can try is to get some 100K ones, physically like the 10K ones you are using. Connect them to the FrSky sensor, then test the response in boiling water and freezing water, making sure the water doesn't come into contact with any wires on the thermistors. If you get readings of 100 deg and 0 deg, then you can use them OK. Freezing water is water with Ice cubes in it, but making sure the thermistor isn't touching the ice itself as that will be below 0 deg.

I think it doubtful a PICAXE can drive the Smart Port directly. The arduino in the openXsensor has to use "bit-bashing" at 57600 baud on a bi-directional signal for the Smart Port (I wrote that part of the code!).

Mike.

Frank Skilbeck27/06/2017 08:00:47
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could you not put a resistor in series to bring it up to 100K write a LUA script to "calibrate" your sensors so you get the correct reading on the display (and voice)

Allan Bennett27/06/2017 08:36:35
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Posted by Mike Blandford on 26/06/2017 22:43:16:

I think you will find the FrSky thermistors are 100K. What you can try is to get some 100K ones, physically like the 10K ones you are using. Connect them to the FrSky sensor, then test the response in boiling water and freezing water, making sure the water doesn't come into contact with any wires on the thermistors. If you get readings of 100 deg and 0 deg, then you can use them OK. Freezing water is water with Ice cubes in it, but making sure the thermistor isn't touching the ice itself as that will be below 0 deg.

I think it doubtful a PICAXE can drive the Smart Port directly. The arduino in the openXsensor has to use "bit-bashing" at 57600 baud on a bi-directional signal for the Smart Port (I wrote that part of the code!).

Mike.

That's good info, thanks. I can easily find 100k (or almost any resistance for that matter) on the RS Components site. So it's worth a try because the straight button type are, to me, much more versatile than the loop type that FrSky supply.

As for PICAXE, I'll certainly not even by trying that route wink

Allan Bennett12/09/2017 19:59:01
1589 forum posts
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I've been away for a while, but a couple of days ago I ordered the FrSky smart port sensor, and the thermistors that came with it measure at 125k at room temperature, according to my meter. I can fit the supplied thermistor to my ESC without too much problem, but I'm going to figure out a bead-on-the-end-of-a-wire solution for my motor -- I may try a 100k version, which are plentiful, and add a 25k resistor in series if necessary. I really only need an over-temperature alarm, so exact values aren't critical as I can set the trigger point appropriately.

Stevo12/09/2017 20:19:27
2699 forum posts
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I've done a fair bit with PicAxes.. Surely once the protocol is cracked it's a matter of programming?

Stevo12/09/2017 20:20:18
2699 forum posts
419 photos

Oops... just seen 75kBaud... ummm....

Edited By Stevo on 12/09/2017 20:20:33

Allan Bennett18/09/2017 19:46:18
1589 forum posts
44 photos

Yes, it looks like you can!

Today I received some 100k glass-encapsulated thermistors from RS Components. I connected one of them to one of the ports in my FrSky smart port sensor, and plugged the FrSky stock thermistor into the other. My limited tests so far show that both of them read 17 degrees Celsius when sitting on the concrete floor of my garage, and both of them get up to about 31 degrees when I hold them between my finger and thumb.

I'll do some more-meaningful checks when I get my transmitter setup sorted -- see my new thread on the problem I'm having -- but since I only want to trigger high and critical temperature alarms, not absolute values, I'll be able to adjust the trigger values if there is any discrepancy.

Allan Bennett05/10/2017 19:42:08
1589 forum posts
44 photos

Update -- test results.

I've finally go around to doing some meaningful tests. I've used the stock FrSky sensor, a 100k thermistor from Farnell, and my laser temperature gun.

In iced water the laser gun read -0.4 degrees, the FrSky sensor 4 degrees, and the Farnell thermistor 2 degrees.

In boiling water the FrSky sensor read 97 degrees, and the Farnell thermistor 99 degrees.

In hot water out of the tap, the laser gun, the Frsky sensor and the Farnell thermistor all read 48 degrees.

It was noticeable that the FrSky sensor took longer to settle down at the temperature, probably due to the plastic sheath around it. The Farnell thermistor also took a very long time to register correctly when put back into iced water straight after the boiling water.

All-in-all the results are excellent so far as I'm concerned, for the range I'm really interested in for my "high" and "critical" triggers is in the region of 50 - 60 degrees.

In the picture below the FrSky sensor is on the left, and the Farnell one on the right. So far as I'm concerned the "pinhead" style of the Farnell one is much easier to use than the FrSky loop: It fits between the grooves in the heatsink on my ESC, and it can be poked inside a brushless motor to rest on top of the stator windings.

Temperature sensors

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