Modifying IKEA Tradfri Sensor (E1525) timeout help wanted

[electrik]

Now that I see the datasheet I am not so sure anymore. It seems the sensor sends a message that is handled by the micro controller after it.

[bob21]

That's a shame. Is it possible to reprogram the controller? I have a CP2102 somewhere.. would this interface with a chip like that?

[electrik]

Than you would have to reprogram the entire chip, and that's quite some effort...

[bob21]

I was hoping maybe it would be a case of connecting via serial and issuing a few commands to set config options. I guess it's not.. Well I can use the sensor in a non-critical area. Thanks for taking a look for me :)

[electrik]

The config options would be overwritten every time by the controller itself, so there is little chance that would work. Or you have to intercept every message to the sensor from the microcontroller...
You could try one last thing and that is finding out where the other legs of the potmeter go to

[bob21]

Hi again,

Ok understood. I have traced the other 2 legs.. One looks like a common between the 2 potentiometers, so input voltage? And the other appears to go to the MCU

https://imgur.com/a/fjbcjA3

[electrik]

Yes, that is what I expected. The voltage level is read by the MCU and used to set options in the sensor. I don't think you can change anything with it. You could try to connect the pin that goes to the MCU, to ground. But no success guaranteed...

[bob21]

I can try - is there a possibility that I could fry it doing that?

[electrik]

if you don't connect VDD to GND, you won't. So you should measure that first.

[bob21]

Gotcha. So we know that pin 4 on the E93196 is VDD, so if I get continuity from pin 4 on the E93196 to either the potentiometer leg or the MCU pin that I am going to be connecting it to, then it's a no go?

[bob21]

Ok, this could be a no go.

Looks like I can get some continuity between these points: https://imgur.com/a/PKPOJdk

So that would be connecting connecting VDD to ground?

But, with a DMM set to 200k, I get a resistance reading of 66.7 between these points: https://imgur.com/a/4K0NPbP because of R12....

Could this be the resistance that is putting that to 60 seconds? Could I connect those 2 green points? Or remove that Resistor and bridge with solder?

[electrik]

Can you measure the voltage on the pin of the MCU that is connected to the potmeter when it is in the lowest position?

[bob21]

Sure, just to confirm though (because I've not measured anything like this before), I put one probe on the MCU pin and the other to ground? Ie. Battery negative? Sorry if this seems like a really dumb question :D

[electrik]

Yes like that. And make sure the meter is on voltage reading, and the plugs are also in the voltage measuring connections. So not in the current measuring ones

[bob21]

I think I may have screwed up one of the earlier measurements. I am using a better meter now, and I got this: https://imgur.com/a/AQk22sR

The Blue pin, which I originally said was connected to the VDD pin appears to actually be connected to the ground shield over the chip - I got a reading of zero. The Red pin, I got a reading of 3V (there abouts) and this is the one connected to the VDD pin on the E93196. Turning the potentiometer did not change the voltage on this.

I remeasured the resistance from the ground leg of the potmeter to top green dot is 77K, bottom green dot is zero when at 1 minute, both are at 77K when at 15 minutes

[electrik]

So is the third leg of the potentiometer still connected to the MCU input on? And what do you measure there? The voltage should change of you change the position

[bob21]

Voltages:

All 3 potmeter legs to MCU (blue): 2.9V - Does not change when potmeter moved
All 3 potmeter legs to MCU (red): ~0.2mV-0.3mV - Does not change when potmeter moved

Resistance:

Top green on potmeter to MCU (red): 67K (turning dial does not change)
Bottom green dot on potmeter to MCU (red): 67K at max time, 110K at minimum time
Unmarked leg to MCU (red): 110K and does not change when potmeter moved

[electrik]

It's confusing me.
The potmeter has three legs. One is positive supply (VDD probably), one is ground and the other one should change voltage of you move the dial. You should measure between ground and the point you want to measure.

Edit
Now you should find out where this third leg is going to

[bob21]

Yeah sorry about that. My inexperience is probably exacerbating things :grimacing: thank you for putting up with me ;)

I am looking at the potmeter, and I think I can fairly say the legs are like this: https://imgur.com/a/1bTBnUo

So with one probe on the variable leg, where to I test with the other probe?

It looks like the variable leg first goes to TP5_1, then to TP5_2, then to the MCU, but it is not clear which pin: https://imgur.com/a/hbgOOBU

[electrik]

@bob21 said in Modifying IKEA Tradfri Sensor (E1525) timeout help wanted:

So with one probe on the variable leg, where to I test with the other probe?

Always to ground

@bob21 said in Modifying IKEA Tradfri Sensor (E1525) timeout help wanted:

It looks like the variable leg first goes to TP5_1, then to TP5_2, then to the MCU, but it is not clear which pin: https://imgur.com/a/hbgOOBU

With the continuity function of your multimeter (when it beeps if you short the probes) you can trace where it goes to.