Suggestions for powering Teensy 3.2 and Prop Shield LC from batteries?

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WShawn

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Hi:

I could use some advice regarding safe voltages to use with my project. None of the other threads I've found address my specific questions.

I'm using a Teensy 3.2 soldered on top of a Prop Shield LC to control a pair of servos, chase LEDs and play some RAW sound effect files for this PKE meter prop I'm working on. I intend to use five 1.2V 2/3A size rechargeable NiMH batteries. These will be recharged through a DC port in the handle from an external charger. This replicates the design of the original prop, so I'm not looking for advice for alternate types of batteries and chargers.

The five batteries read as 6.3-ish volts when charged. If I put a 1N4001 diode in series with them the voltage drops to 6 volts, right at the upper limit of what a Teensy 3.2 can safely handle (note that I'm never trying to power the Teensy from these batteries while I have USB plugged in).

It would be nice if I could just run the + from my batteries (via the diode) to the Vin of the Teensy and the - to ground, but what would that full 6V do to the Prop Shield LC, which I believe is rated for only 5V?

If I risk damaging the Prop Shield with 6 volts should I run my batteries through a 5V regulator like an LM350T5? My research indicates that the input voltage should be more than 2 volts above the regulator's, but I don't know if that's applicable here.

If the 5V regulator isn't appropriate should I use something like a LD1117V33 that would drop the voltage to 3.3V? Would such lower voltage result in a lower volume of my sounds?

Are there other approaches I should be investigating? In my old totally analog version of this prop I used a 1000 µf capacitor bridging the + and - power to smooth out the power when the servos would kick in. I was sort of assuming I wouldn't need that in this setup with a Teensy.

In either case I'd send all 6 volts of my batteries to the servos to ensure I get their maximum speed.

My breadboarded prop draws maybe 140-160 mA when the LEDs are chasing and the sound is playing. When the servos briefly kick in to deploy or retract the arms that jumps to 220 mA or so.

Thanks for reading.

Shawn Marshall
 
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I think you don't need an extra regulator for 5V.
As you discribed the max. voltage via diode and full charged batterys is 6V.
The 74AHCT1G08 is rated up to 7V max. supply voltage and the LM48310 is rated up to 6V max. supply voltage.
 
larry_berlin said:
I think you don't need an extra regulator for 5V.
As you discribed the max. voltage via diode and full charged batterys is 6V.
The 74AHCT1G08 is rated up to 7V max. supply voltage and the LM48310 is rated up to 6V max. supply voltage.
Click to expand...

Thanks for taking the time to reply, Larry. You're right about the max tolerances shown in the data sheets. I guess I'll have to decide whether I want to risk running the amp beyond the recommended 5V. It's not like this thing is going to be running constantly for hours at a time. Over the course of a day, say like at Rose City Comic Con, it would probably be active for less than an hour, on and off.

Would I assume that the flash memory (W25Q64FV), which is rated at 4.6V maximum, gets regulated power from the Teensy (3.3V)?

Best.

Shawn
 
Well you could use a step-up/step-down voltage regulator if you are unsure about the power level (particularly with batteries that start out freshly charged over the spec, but then reduce their voltage over time). According to my notes, based on some of Paul's postings, the LC is only rated to 5.5v, and the max you can draw from the LC (or from the USB that connects to the LC) is 350ma.

Here is one from pololu.com. You can select either 3.3v or 5v, and it has a low voltage cut-off. If the voltage is near 5v, you can get about 1.5a from it. Do note that some regulators can run hot, particularly if the voltage is wildly different than the output:


Note, when I wear my wooden bowtie with neopixel rings or uncanny eye goggles, I tend to have them running for several hours continuously. So, you might want to think whether the 1 hour is realistic. If at all possible, plan for being able to change batteries.

I tend to like being able to charge the battery in place. My normal method is to use LiPo batteries and use the onehorse chargers:


Alternatively if you are careful with the placement, you can mount the Adafruit Teensy/Feather adapter along with the prop shield and Teensy 3.2. The Feather adapter includes a lipo charging circuit. One thing I don't like about the Adafruit adapter is it doesn't have an off switch for the battery. The onehorse adapter having the on/off switch is more convenient:

 
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