What are the voltage requirements: are there upper and lower limits?
The silkscreen on the Riffle says 3.5v to 6v for the "general" power connection. That's different from typical 328p Arduinos (e.g., Uno, Nano) which can be powered by 7v to 12v. Maybe @donblair can confirm the range (oops, he won't see this because this is not a comment).
How many AA/AAA equivalent batteries do you need to use, and can those be rechargeable?
So assuming 3.5v to 6v, the Riffle can use four AA or AAA batteries. Four alkalines would supply 6v, and four rechargeable NiMH (e.g., eneloop) would supply 4.8v (when the batteries are fresh).
Can commercial lithium rechargeable batteries like these be charged from the Riffle's JST circuitry?
Don't know. Those require a special size battery case -- they are not AA or AA. You might want a dedicated charger.
How does JST work with conventional batteries? What are the easy methods and expert methods to attach JST connectors to batteries?
You can buy battery cases for AA and AAA batteries with JST connectors. For the Riffle you want JST ph 2-pin. It might not be easy to find a four battery case with a JST ph 2-pin connector. But cases are just a couple of bucks and JST connectors are cheap too.
4 AA case at Adafruit, $3.00: https://www.adafruit.com/products/830
Above: Case for three AA batteries with JST ph 2-pin connector from Adafruit (left), case for four AA batteries from eBay (no connector) and a wired JST ph 2-pin connector which can be soldered on (right).
I bought some JST ph 2-pin connectors but they don't quite fit in the ones on the Riffle. It was easy to shave the plastic so it fit. You can buy a few here.
Thank you for this informative answer! I have a few followup questions.
On the adafruit description for their 3 x AAA enclosure, they say that it is a good stand-in for their 3.7 V lithium battery, with estimates of a voltage ranging from 3.7 V for fully charged NiMH batteries to 2.7 V at their end-of-life.
Would it be safe to use the Riffle in this configuration, or would the Riffle start to suffer when the battery voltage dips down past 3.5 V? E.g. does the silkscreen label refer to nominal voltage, or actual voltage?
Maybe we don't know yet, and have to characterize the riffle's performance still.
Also, 4 x AA or AAA batteries would give a voltage of 6 V, which is right at the Riffle's stated upper limit. I assume that higher voltage than this could be dangerous for the riffle's electronics, but 6 V would be safe, and perhaps the longest-lasting option for battery life?
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