RE: Low-Power Wireless: Building an Outdoor Transmitter!

shabaz — Wed, 02 Sep 2026 20:44:16 GMT

Regarding the issue that reset would not automatically occur after programming, I just tried this mod:

Basically, Q1 was the PNP transistor, that's been replaced with the P-ch MOSFET, and R7 upped to 100k, and added C22 in series with R6, but also shunted that with a 1 Mohm resistor.

The idea was to make the BSL_INVOKE line go high only briefly, rather than keep it held high during programming, therefore allowing the microcontroller to reset at the end of programming, without going back into bootloader mode.

It does work, but I don't know how reliable it will be.

Here is what I see on the Q1 gate (yellow) and Q1 source (red), when the mspm0_programmer.py is started.

This shows the Q1 gate again, and the BSL_INVOKE line (red). Nice pulse I guess.

The screenshot below shows Q1 gate again (yellow), and the MSPM0 *RST line (red). Not happy it is going to 4V. I believe a fix for that could be to add a diode in series with the *RST line, so the CH340K can only pull it low. I still need to try that.

The multiple pulses are probably because the programmer code enables and disables the *DTR and *RTS lines a few times at the beginning, it seems to be a driver thing (I didn't get reliable results in the past without that). Whether all this works with (say) Linux/Mac, and on different speed PCs, I have no idea!

In summary: With this mod, I can program the MSPM0, and have it restart automatically, all under control of the USB, no boot or reset buttons need to be pressed. And I can access the user menu using TeraTerm, provided it is set up as shown below (see the DTR setting) again just under USB control, no button-press etc. But with that caveat, that this might not work for all setups.

RE: Low-Power Wireless: Building an Outdoor Transmitter!

shabaz — Tue, 01 Sep 2026 21:44:39 GMT

I made two of the outdoor transmitters, one will be a test unit, so I put that in an enclosure before I accidentally damage the delicate antenna.

If I had thought things through properly, I'd have made the PCB shorter, so I could have put the antenna on the end panel (at least 5 mm of clearance is needed from any ground plane).

By chance I had some light pipes, they make quite a visual improvement rather than peeking down the LED holes. Red indicates the CC1101 is powered up, and the blue flickers on when transmitting.