The MQTT letterbox Part 2: Sending alerts from MQTT // Project


So that the battery would start out fully charged I left it overnight connected up to my bench power supply limited to 160mA current and 6v. So, how well does it work?

First a mail delivery test. Cool!

And what about checking the rear flap? A bit of a delay, but still pretty good.

So, there we have it. A pretty simple setup. I ended up spending more on this than I originally intended, but I think the end result was worth it. Leave a comment below if you made one yourself and any improvements you might have made.

In a followup video I’ll be looking at battery optimization, because there could be some weeks where there’s not enough sun to charge the LiPo and it’d be good to be able to get a full week out of a single charge.

I’ve also created a tutorial of this video on and entered it into the IoT competition. So, if you liked this project head on over to and vote on my project.

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