Problem with DIY OTG (USB variant)

[basanca]

Hi

I have a DIY OTG (USB) which connects to OTMonitor but doesn't respond. So i did the measurements accordingly to http://otgw.tclcode.com/debugging.html#power
My level of experience with electronics is beginner level
Unfortunatly I have soldered the IC without the socket. So it is impossible for me to get the IC out.

steps to follow:
The first thing to check is the power supply. Start out with the gateway unplugged from mains power, thermostat and boiler disconnected, and the IC's removed from their sockets. Now measure the resistance between the two terminals of X3. This should be in the order of kΩs.
My value is 3.11 kOhms
Check for 5V +/- 1% between pins 5 and 14 of IC1
4.9V with correct polarity
Next measure the voltage on X1. This should produce a value somewhere between 18V and 34.5V
23V
f the voltage is correct you can measure the current between the two terminals of X1. It should be between 5mA and 9mA.
15.4mAh
If you connect pin 3 of the IC1 socket to ground (e.g. pin 5), the current between the two terminals of X1 should be between 17mA and 23mA
20,5mAh

Now use two pieces of wire to connect X1 to X2 and plug the mains power back in. You should now find a voltage between 15V and 18V on X2 (and X1).

16.75V
If you connect pin 2 of the IC1 socket to VDD (e.g. pin 14), the voltage on X2 should drop to between 5V and 7V.
5V
Measure the voltage on pin 18 of the IC1 socket with pin 3 left open and again when it is connected to ground. In the former case the voltage should be below 1.25V (it is actually expected to be 0V). In the latter case the voltage must be above 1.25V (and will probably be close to 5V).

Don't really understand what "with pin 3 left open" means

If you see nothing at all and you have checked your serial connection to the PC, verify that the PIC is really running. You should measure the following voltages on IC1: pin1=1.25V, pin2=0V, pin3=4.5V, pin4=5V, pin8=5V, pin9=5V, pin10=5V, pin11=5V, pin12=5V, pin13=5V, pin17=3.5V

pin01: 1.02V
pin02: 0V
pin03: 4.14V
pin04: 4.14V
pin08: 3.8v
pin09: 3.8v
pin10: 4.12V
pin11: 4.12v
pin12: 4.12V
pin13: 4.96V
pin17: 2.6V

Hope somebody can pinpoint me in the right direction

[hvxl]

Something is clearly wrong, but it's hard to say exactly what. Some of your measurements make me doubt the 5V power supply. Can you determine if it's stable? Does the reading fluctuate if you measure over a longer period of time? Do you get a reading of more than a few millivolts when you set your multimeter to AC?

Do you know which firmware is loaded in your PIC? Assuming it's the latest regular firmware, what do you see when you power up the OTGW with the USB connector plugged into your PC and otmonitor connected? Do you get the "OpenTherm Gateway 4.0.1" message? Do you have LED's connected? Do they briefly flash after power up?

If neither of those happen, your PIC may not be running its program. That may also be the cause of the bad current reading you found.

[basanca]

hi hvxl,

thx for your support.
I re-meassured again, and these are the new outputs
in same order as previous post
-3.00 kOhms
-voltage fluctuates between 5.05 and 5.75
-23.3v
-6.3mAh
-20.6mAh
-16.60v
-5.05v

so all the readings are now correct, except the Pin5/14 ic1 is fluctuating.
Still no output within OTMonitor.
I don't have the leds unfortunatly.
when i meassure X1 with AC, i see some fast fluctuations in the beginning
Hope this info will clarify my problem.
thanks in advance

bas

[hvxl]

-voltage fluctuates between 5.05 and 5.75

That's very wrong. A 7805 should be able to keep the voltage stable within 0.1V. I'm not surprised the PIC doesn't operate well with such an unstable power supply. Maybe your 7805 is broken, or not soldered correctly. Also check C1 and C2.

[basanca]

hi,

Before i did anything, I thougt it would be best to remeassure again. And now i have the same results as the first readings. So a stable 4.9V at X1 and a 15.4mAh at X1.
I did also meassure C1 and C2. (well, what i think c1 and c2 are )

I made a picture so that it is clear we talk about the same

mediafire.com/view/y1zb1zozju1pzwv/Stud ... 094829.jpg
C1 was 0.9v
c2 was 0v

update: yet again plugged it in and remeassured:

Again fluctuations on pin5/14 and good current at X1

I will buy a new 7805 and let you know how that worked out.

thx

[hvxl]

With C1 and C2 I was referring to the two electrolytic capacitors marked, ehm ... C1 and C2. I am clueless how you came up with your idea of C1 and C2. And by checking them I meant making sure they are soldered correctly, not measuring a voltage.

[basanca]

ha, Told you I was a beginner

[honeywell]

-voltage fluctuates between 5.05 and 5.75

That's very wrong. A 7805 should be able to keep the voltage stable within 0.1V. I'm not surprised the PIC doesn't operate well with such an unstable power supply. Maybe your 7805 is broken, or not soldered correctly. Also check C1 and C2.

Hello Schelte,

I had the exact same problem. This may be due to the fact that a low power (L = 100mA) version of the 7805 was shipped with the kit that I ordered from http://www.opentherm-gateway.com. After replacing it with a regular 7805 (1A) everything works as expected. That said, it is supposedly bad practice to have a very high difference between input and output voltage of a 7805 voltage regulator - and the design of the gateway is such that it *is* high (24V input, which is close to the maximum, see for example: http://www.ti.com/product/ua7805?CMP=AFC-conv_SF_SEP - I read somewhere that it advised is to have about 3V difference, which would be 8V)

Regards,
Tom

[hvxl]

Let's not duplicate the exact same conversation in multiple places. Discussion continues here.