OTGW does not connect to iSense thermostat

[Arten]

Hi all,

Last weekend I assembled the Wifi OTGW board from nodo-shop.nl. I have it connected using the NodeMCU and I am able to receive information from the boiler (Remeha Tzerra). However the iSense thermostat give the f203 error (and the backlight does not work). when I connect only the iSense to the OTGW board and check the log in otmonitor no data is received at all from the thermostat. I measured the thermostat connector on the OTGW and it showed ~23volt.

Do you guys have any idea what is wrong?

Thanks a lot in advance!

Maarten

[Arten]

i've done some more power tests. The current between the terminals of the thermostat port is about 7mA and if i connect pin 3 of the IC1 socket to ground (e.g. pin 5), the current between the two terminals is about 19mA. With thermostat and boiler connected to each other I get 17.2V between the terminals and when pin2 is to VDD it nicely drops too 6.7V.

However the only thing it does not seem to do well is the test were I measure the voltage on pin 18 of the IC1 socket with pin 3 left open and again when it is connected to ground. I measure 3.3V where it should be below 1.25 and 5.13V where it must be above 1.25V.

EDIT: Is made a mistake during the last check.. i is actually totally fine as wel....

I am pretty lost now what could be the cause....

cheers,

Maarten

[hvxl]

The voltages you measure on pin 18 are a problem, but not the first one. You indicate no messages from the thermostat are reported. Even with the pin 18 problem, you should get those. So let's start with that first. With thermostat and boiler connected to each other, measure the voltage on pin 17. Based on the voltages you reported, pin 17 should be at 2.14V. Then when you connect pin 2 to VDD, it should drop to 0.84V.

Given that no messages are received from the thermostat, combined with the incorrect measurement on port 18, I suspect you may have mixed up two resistors out of R4, R5, R6. The most likely mix up would be R4 (orange/orange/brown) and R5 (orange/orange/orange). If that's the case, you would end up with 16V on pin 17. That's above the maximum allowed for the PIC, so hopefully you didn't blow up the input pin.

[Arten]

Thank for the reply! I'm sorry for the confusion, it seems I was wrong about the voltage measured on pin 18. It seems actually to be fine.

I measured the voltage drop on pin 17 when I connect pin 2 to VDD. It seems to drop from 2.12v to 0.76v.

If there is any mixup in resistors it was then already on the board. the OTGW board I have is the OpenTherm WIFI Interface v2.0 from Nodoshop. I checked the resistance for R4, R5 and R6 that one seems OK when I measure them with my multimeter.

As I said earlier, messages from the boiler are received fine..

Thanks again for your help!

Cheers,

Maarten

[hvxl]

Wait a minute! Are you saying you see boiler messages with the iSense connected? That would mean the OTGW incorrectly determined that there is no thermostat. It should report that fact. But you may not see that because the NodeMCU takes time to boot up itself and connect to WiFi.

With both the thermostat and boiler connected, please collect a log where you issue a GW=R command. That only restarts the PIC, so you can see everything it reports from the start. If at some point it blurts out "Thermostat disconnected", then that's the cause of the behaviour you're seeing. But it would mean that some voltage level from iSense is outside the expected levels for opentherm.

You can further analyse such a case by loading the diagnostic firmware and running test #5.

[Arten]

Sorry for the late reply,

i've found some time to check the logs after resetting the gateway:

11:32:00.182930 ÿOpenTherm Gateway 4.2.5
11:32:00.210047 Thermostat disconnected

Other than that I don't get anything.. It seems it also does not communicate with the boiler now (as it did properly before ). I measured the thermostat output and it does give short bursts of signal (see attachment). the voltage measured with my multimeter is quite low though (5.4 volt).

I'll check the board again later today to see if there something wrong with the soldering...

best,

Msarten

[Arten]

Oke so boiler messages are logged again:

13:02:44.293108 ÿOpenTherm Gateway 4.2.5
13:02:44.317454 Thermostat disconnected
13:02:45.261488 R80000100 Read-Data Status: 00000001 00000000
13:02:45.353018 B4000010C Read-Ack Status: 00000001 00001100
13:02:46.300268 R80190000 Read-Data Boiler water temperature: 0.00
13:02:46.442190 BC01945CC Read-Ack Boiler water temperature: 69.80
13:02:47.341560 R10015A00 Write-Data Control setpoint: 90.00
13:02:47.447946 BD0015A00 Write-Ack Control setpoint: 90.00
13:02:48.376241 R00060000 Read-Data Remote parameter flags: 00000000 00000000
13:02:48.469402 BC0060303 Read-Ack Remote parameter flags: 00000011 00000011
13:02:49.416935 R00110000 Read-Data Relative modulation level: 0.00
13:02:49.558543 B40113800 Read-Ack Relative modulation level: 56.00
13:02:50.454372 R001B0000 Read-Data Outside temperature: 0.00
13:02:50.561549 B601B0000 Data-Inv Outside temperature: 0.00
13:02:51.491846 R801C0000 Read-Data Return water temperature: 0.00
13:02:51.583859 BC01C39B5 Read-Ack Return water temperature: 57.71
13:02:52.531585 R900E6400 Write-Data Maximum relative modulation level: 100.00
13:02:52.670694 B500E6400 Write-Ack Maximum relative modulation level: 100.00


but still no thermostat.

[hvxl]

As I indicated before, if the OTGW reports "Thermostat disconnected", it determined that there's no (opentherm) thermostat connected. It looks like it thinks there's on on/off thermostat connected, in the on state! That's why it sends a status message with the CH enable bit on and a control setpoint of 90°C.

You can try to issue the command DP=57 a few times. That will report the A/D value measured on pin 17. It should be above 6, but the logs suggest it's below.

[Arten]

Thanks again for all your help! Great to get such good advice!

I issued the command and it reported DP=00 every time. measuring PIN 17 show 0.64volts and on my scope I see that there is a signal (from the thermostat?) but it is quite low (see attached). do you think there something wrong one of the

I'll try tomorrow if I can do some more tests with the diagnostic firmware.

cheers

Maarten

[hvxl]

That signal looks fine. It has a 1.3V difference between the low and high levels. And if the low level is the 0.64V you measured with your voltmeter (the line is at the low level most of the time), then the levels are perfect. So it is strange that DP=57 always reports 00. 0.64V should result in 0x21 (33) or thereabouts.

This sounds like the A/D converter of your PIC may be faulty. The diagnostic firmware should provide more clues.

[Arten]

Ok I loaded the diagnostic firmware on the OTGW and I get:
Thermostat: 0.00
Boiler: 3.51
Reference: 1.22

Am I right in saying that the A/D converter indeed is not working correctly?

Cheers,

Maarten

[hvxl]

Was this test done with the thermostat connected? Because then you should see 2 values for the thermostat.

There is actually only 1 A/D converter in the chip, with a multiplexer to be able to measure the analog voltage on 1 out of 7 I/O pins. The A/D converter doesn't seem to have any problem with measuring the voltage on AN2 and AN3. Only AN0 gives 0V, which does not match your manual measurement. So, the actual A/D converter function looks to be OK.

When you measure the voltage on pin 17 by hand, do you measure on the actual pin of the PIC? I ask because this sounds like there may be a bad contact between the IC socket and the PIC pin. That can easily happen when a cheap IC socket is used.

[Arten]

It is with both boiler and thermostat added. I measured the voltage (0.64v) on the pins of the chip themselves (just repeated it while running the diagnostic test). When I connect only thermostat the same happens.

I am sorry that cannot provide more information.

cheers,

[hvxl]

Then I'm afraid that the only remaining conclusion has to be that the I/O pin is blown.

[Arten]

Hmm I faired that would be the case... I guess ill have to find a replacement then...

Thanks again for your in help!

Best

Maarten