USB battery backup: shield vs smartphone backup

I’ve decided that due to a limited demand for my IoT product, I’m gong to release the product using photon’s (not P0 or P1’s). Product requirements are battery operated for 12 hours of operation without recharge. I was considering a power shield with battery, but since my project needs a minimum of 4 independent batteries, I’m considering using a smartphone rechargeable backup battery pack (that’s what I’m using now for a prototype).

Is there any reason I couldn’t use the smartphone battery backup in my project?

@harley, there is no reason except that you need to ensure that your battery pack doesn’t shut down if too little current is drawn by the Photon, which typically happens during deep sleep. You could also use a resistor divider and monitor Vin to put the Photon to sleep if the voltage from the battery drops too low but I suspect this won’t be an issue in your application.

Voltaic systems has USB battery packs that have the ability to not shut down if low current draw is detected from the connected USB device.

My application is a dog race timer using two posts with 3 IR emitters on one pole and 3 receivers on the other pole to accommodate the size of the dog and the obstacle that starts and completes the course. All three of the emitters are fed from the 3.3 V output of the photon. Also, the emitters have a modulated signal created by using a PWM pin feeding a MOSFET. The receiver pole has three IR receivers which are fed by the 3.3 V output of the photon. I hope there is enough power output from the 3.3 V to power all three emitters and receivers.

AND… I’m hoping that power draw will keep the battery from shutting down from low power draw… OOPS :grimacing: I just realized that the way the receivers work is that they are fed 3.3 V on one pin and when the emitter beam is not aligned, another pin stays high. When the beam is aligned, that pin drops to zero. Therefore, on a perfectly aligned timer, there is only the power draw of the photon itself. That photon sends a UDP message as a keep alive every 1 second. In past experimentation, one of the external batteries I used shut down when that’s all the photon was doing.