[OpenTRV-dev] Help getting serial connection to Radbot

Mon Feb 15 10:21:28 UTC 2021

Fantastic, that’s good to know! 

I think the 50ma figure for the 3.3V rail is very old, but they never published updated numbers for newer models. See also Raspberry Pi Power Limitations - Raspberry Pi Stack Exchange <https://raspberrypi.stackexchange.com/questions/51615/raspberry-pi-power-limitations>  and Piversify — Exploring the 3.3V Power Rail (tumblr.com) <https://raspberrypise.tumblr.com/post/144555785379/exploring-the-33v-power-rail> . The latter pushed it to 800mA. So, I think we can recommend people go for this simple solution as long as they are not powering anything else from that rail while injecting the key.

Cheers,

Christoph

From: OpenTRV-dev <opentrv-dev-bounces at lists.opentrv.org.uk> On Behalf Of Robert May
Sent: 14 February 2021 23:26
To: Closed list for developer discussions <opentrv-dev at lists.opentrv.org.uk>
Subject: Re: [OpenTRV-dev] Help getting serial connection to Radbot

Regardless of what else changed I can't make it work with my (cheap) CH430 USB dongle (similar to this one: https://www.ebay.co.uk/itm/3-3V-5V-Serial-Adapter-Module-CH340G-USB-to-TTL-6-Pin-UART-Adapter/192935577926?hash=item2cebdb4946:g:RFsAAOSwyXNZ-mJr).  It works fine with the PI's built in serial port, so no actual dongle needed at all.

To use the built in serial port you need to stop the PI using it for boot messages and attaching a terminal to it:

sudo raspi-config;  Select option 3 Interface Options, and then Option P6 Serial port;  Answer 'no' to the question "would you like a login shell to be accessible over serial?", and 'yes' to "Would you like the serial port hardware to be enabled", and then reboot.

Then connect Physical pin 8 (TxD) to TX pad on Radbot and physical pin 10 (RxD) to RX pad on radbot.   COnnect one of the ground pins (e.g. physical pin 6) to the -ve terminal of the radbot.  and start a terminal on /dev/ttyAMA0

Either screen (if you have it installed): screen /dev/ttyAMA0 4800. (Ctl-A k to kill the session and exit)

or microcom (installed in base image):  busybox microcom -s 4800 /dev/ttyAMA0 (Ctrl-X to exit)

If it's safe to power the Radbot from 5V then it could be powered from the PI, but not from the 3.3V rail if the motor unit's attached (usually OK to get at least 300mA from the 5V rail, but only 50mA allowed from the 3.3v rail - source: https://www.circuits.dk/everything-about-raspberry-gpio/#:~:text=The%20total%20maximum%20recommended%20current,the%20rest%20of%20the%20board. ).  If my memory serves me I was seeing about 160mA draw when the motor was running.

Rob.

On Sun, 14 Feb 2021 at 23:01, Tristan Keen <tristan.keen at gmail.com <mailto:tristan.keen at gmail.com> > wrote:

Glad to hear you got there!

  My USB/Serial cable (link in Part List wiki page) was outputting 4.9 V open circuit from the "power" connections, so I presume it was connected to the USB main power output.  Originally I tried powering the Radbot via a couple of low value (82 Ohm) resistors as I was a bit nervous of driving it at the higher than expected voltage, but couldn't connect reliably.  After checking the Atmel 328P's datasheet, which suggests a 2.7 - 6V range, I removed the resistors and tried again - it worked.  Voltage dropped to 4.4 volts or so when the motor came on during its initial valve cycling though.

So far all four appear to be unharmed...

Tristan.

On Sun, 14 Feb 2021 at 22:26, Robert May <rob at themayfamily.me.uk <mailto:rob at themayfamily.me.uk> > wrote:

Thanks all.  I'm there (or at least I think I am).

I changed a number of things - the voltage I'm driving the Radbot (now at 3.3v), I remade my solder connections and replaced the wires/connectors as I think one of the dupont connectors was loose, and I moved to using the built in serial port of the PI (/dev/AMA0).   I'll see if I can work out which of these was actually the culprit.

Out of interest, what is the max voltage that is safe to run the Radbot.  If I understand this page correctly (https://github.com/tyrken/heatmon/wiki/Reprogramming-Radbot-TRVs) then it is suggesting powering it at 5V (direct from the USB port)

Onwards.

Rob.

On Sun, 14 Feb 2021 at 21:45, Damon Hart-Davis <dhd at exnet.com <mailto:dhd at exnet.com> > wrote:

Hi,

1) FWIW, when I am powering remotely, eg to reflash, I tend to run at 3.6V.

2) Yes, I think that we label our TX and RX the ‘wrong’ way round and have confused ourselves from time to time.  Almost certainly an early error or at least bad choice by me, reinforced by my trying to then be consistent across schematics.

3) FWIW I use a FTDI TTL-232R-3V3 to talk to Radbots.

Rgds

Damon

On 14 Feb 2021, at 20:52, Robert May <rob at themayfamily.me.uk <mailto:rob at themayfamily.me.uk> > wrote:

Thanks Damon, Christoph.

I already moved to soldering my connections to eliminate that issue.

I can see the TX LED flash on my dongle when I hit <return>, and if I swap the tx/rx connections so I have tx on dongle to tx on Radbot and rx on dongle to rx on Radbot then after I hit <return> I see the rx led on the dongle flash approx. every 2 seconds for a while - so I *think* I'm waking it up.    This feels wrong, but past experience tells me that there is sometimes confusion over how rx and tx pins are marked.

But I see nothing in my terminal.  I've shortened the wires as much as I can, and I'm sure that my grounds are OK

Can you expand on what you mean by "perhaps one of the devices doesn’t like the 3.0V supply"?

Here's a couple of pictures

https://www.dropbox.com/s/s8jdv6j9a4covw3/Photo%2014-02-2021%2C%2020%2041%2054.jpg?dl=0

https://www.dropbox.com/s/sp819pw2ds1lf73/Photo%2014-02-2021%2C%2020%2042%2011.jpg?dl=0 (not a good shot, but I'm sure the pins and +ve terminals are not touching)

Any other ideas?  I've been staring at this all day and can't see what's wrong.

Rob.

On Sun, 14 Feb 2021 at 19:33, Christoph M. Wintersteiger <christoph at winterstiger.at <mailto:christoph at winterstiger.at> > wrote:

Hi Rob,

That’s great, you’ve got very far in a very short amount of time! 

It sounds like you’re “holding” the wires on – just solder them on if you have a soldering iron around, it’s easy enough to take them back off after the operation.

I can imagine that there’s a ground potential problem and perhaps one of the devices doesn’t like the 3.0V supply. The Radbot takes very little power and I was able to simply power it from my USB-serial adapter, but that depends on the adapter of course. Alternatively, the RPi also has a 3.3V supply (and 5.0V too) and it has a serial port right next to the supply pins too, so if you have a few breadboard wires around, that would be a simple and quick alternative.

Cheers,

Christoph

From: OpenTRV-dev <opentrv-dev-bounces at lists.opentrv.org.uk <mailto:opentrv-dev-bounces at lists.opentrv.org.uk> > On Behalf Of Robert May
Sent: Sunday, 14 February, 2021 18:24
To: Closed list for developer discussions <opentrv-dev at lists.opentrv.org.uk <mailto:opentrv-dev at lists.opentrv.org.uk> >
Subject: [OpenTRV-dev] Help getting serial connection to Radbot

I've finally found time to unbox my Radbots.   The plan is to build a combined stats hub and boiler controller based on a RPi.

I've successfully compiled the code Christoph shared (https://github.com/wintersteiger/wlmcd) and used to to show the one Radbot I've powered up transmits and that I can receive the frames using a CC1101/RPi combination.  Of course the decryption fails as I've yet to set a decryption key.

I'm struggling to get a connection over the serial port to the Radbot.  I'm trying to follow the instructions shared by Tristan (https://github.com/tyrken/heatmon/wiki/Reprogramming-Radbot-TRVs) but I can't seem to get any comms over the serial port.

I've opened up my radbot to get better access to the pads.

I'm powering the Radbot from a bench power supply at 3.0V

I've got a USB serial dongle operating at 3.3V logic, grounded to the -ve supply.

I think I'm hold the rx/tx lines on the pads (tx from my dongle to rx on the radbot and rx on the dongle to tx on the Radbot), but I get nothing from 'screen' that I'm using for my terminal.

As far as I know I'm using 4800baud, 8-N-1 (screen /dev/ttyUSB0 4800), which I believ to be the expected settings?

Can anyone see anything that I'm doing wrong or give me a pointer to things that I can try. ?

Thanks,

Rob.

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