Cable to attach to update ID


Just to confirm before I order one, is this what I need to be able to update the ID on an emon TX?

I have a TLL to USB knocking about, I assume i cant use that.

That’s exactly what you want. Be careful which way you connect it - GND is at the RJ45 end on the emonTx.

Ok ill get one ordered, thanks


Enter ‘+++’ then [Enter] during the POST (Power-On Self-Test) 10s delay during startup to enter node ID config:

See this post for more details how to update node ID via serial config:

I’m not sure I’ve ever seen a TTL to USB that wasn’t also a USB to TTL… Maybe provide a picture of what you’ve already got?
They’re usually bi-directional…

If the output is true TTL (i.e. 5 V) and as the emonTx inputs are constrained to 3.3 V, I see the possibility of a destroyed Atmega in your emonTx - and it’s no longer a plug-in replaceable part. Unless you know it will be safe, it is not worth the risk. Apart from which, we’ve had reports that some that are supposed to be suitable have not worked.

Also I have TTL to USB’s that do not have a reset line.

ATmega328 inputs are 5V tolerant, the programmer sold via the shop is 5V. No problem using a 5V programmer.

I think many programmers (including the shop sold one) are auto-detecting and safe for use with 3.3v or 5v.

AFAIK the ATmega328 inputs are NOT 5V tolerant when VCC is 3.3v (see Are any ATmega328P input pins 5V tolerant when VCC is 3.3V? - Project Guidance - Arduino Forum and atmega - Why can't the atmega328p accept 5 and 3.3v signals at the same time? - Electrical Engineering Stack Exchange)


All of those reasons are precisely why I said:

I did originally have all of the stuff about 5V vs 3.3V etc. in the post, but I took it all out and asked for the picture instead.
I also did notice that the shop one is rated 5V. The ones I have (not from the shop) are 5V and 3.3V based on a jumper.

The expensive Adafruit ones (for example) have 5V power and 3.3V logic (so that they work with both 5V and 3.3V devices), which may be what you mean by “auto detecting”? It isn’t actually auto detecting though :slight_smile:

As are my FTDI one’s, BUT when you inspect the tracks (on mine), the jumper only changes the Vcc out pin, not anything on the adapter board. The common jumper pin is connected to the header’s Vcc pin alone and the other 2 jumper pins are connected to the 3.3v and 5v rails.

I always set mine to 5v to power an emonTx, whilst the adapter is connected serially at 3.3v levels as the emonTx is actually running at 3.3v. This is how the shop “5v” adapter works with a 3.3v ATmega328 on a 5v emonTx.

The point I was making was the adapter is safe for use on 3.3v and 5v processors. the processor is NOT 5v tolerant when running at 3.3v, The 5v supply to the emonTx header causes enough confusion as some users are not aware the device is running at 3.3v not 5v, to say the device is 5v tolerant because you can connect an adapter that outputs 5v Vcc is misleading and needed clarifying.

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Thanks, I have it ordered from you