full disclaimer: total noob here.
trying to make a midi controller to add functionality to a drum machine, a roland tr-09 using a teensy 3.5.
my plan is to power the teensy through a 6v power supply, then send midi via usb to the usb port in the tr-09, which would ALSO power it (or so i hope). the tr-09 runs on 4 AAs or, more usually i guess, via usb. 4 AAs = 6 v.
It depends on your AA batteries. Non-rechargeable AA alkaline/lithium batteries are only 6v (i.e. each battery is 1.5v) when they are fresh. As you draw down the power drops. This is how the simple minded battery level gauges work -- the see what the voltage is currently reading to tell you what the charge level is.
Rechargeable Nimh/lithium ion batteries in AA form tend to be at 1.2v per battery (i.e. 4.8v). The battery delivers 1.2v for a longer period of time before starting to drop the voltage.
If you use lithium ion batteries directly, they tend to deliver 4.2 volts initially and drop to 3.7 volts for most of the discharge. Note, if you put the common battery chargers in the circuit, many of them are limited to 5.5 volts of power, so a 6 volt surge might damage them.
So if you are using something that is voltage sensitive, you probably need to have a voltage regulator. The Teensy tends to prefer 3.5 to 5.5 volts. It depends on usage, etc. whether 6 volts would fry the Teensy.
However, given the cost of the TR-09 vs. the Teensy, I would think you don't want to go messing around trying to power the TR-09 from a Teensy.
Three thoughts come to mind. Note, I am a software guy, not a hardware guy. Theses suggestions come from watching the group, and doing some powering of Teensy systems:
- One way to power the system, is provide separate power to both the Teensy and the TR-09. Here it is critical to make sure the two machines share a separate ground (i.e. run a wire from the ground of the TR-09 and connect it to the normal ground pins of the Teensy (not the analog ground pin between VIN and 3.3v).
- The other way is to power the TR-09 normally, and use the power from the TR-09 to power the Teensy. Here you might need to disconnect the Teensy from the TR-09 when programming it.
- You could use isolation methods (optocouplers, etc.) so that the Teensy and TR-09 don't share any power.
I tend to like pololu's 5v voltage regulators that are step-up and step-down, which means you can feed them 3v input or 12v and it will produce 5v output. Assuming you aren't trying to drive high powered devices, something like this might work for you, sitting in between the TR-09 and the Teensy, drawing power from the TR--09 and converting it to 5v for the Teensy.
https://www.pololu.com/product/2119
