Check my thinking:
I’m building a Thermal Detonator - very simple - 4 x 3mm LEDs plus sound.
I plan to use a Proffie 3.9 with the 500mAh battery below and just use the on-board Proffie USB to charge it. I’ll set up a charging preset that pips one LED every seven seconds to show it’s in charge mode, as the main TD switch will basically just boot up the Proffie (I’ll have a concealed AUX switch inside just to switch presets).
Can I just double-check with the wise here that this will work safely with no need for any extra charge module or anything like that?
Thanks in advance. 
Should be fine.
On mine, the slider is one button, and the red LED is another button.
Once it blows up, you can switch presets using the red button.
You could also do something silly, like turning it on upside down goes to the next preset or something.
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Thanks Prof. It was the charging I was mostly concerned about.
And your TD sounds a little more sophisticated than the one I’m building. As long this one is safe and makes the sound and the lights, it will be mission accomplished.
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Mine is fairly simple, and does not have a lot of bells and whistles.
The only complicated part was making the red button actually work as a button.
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