Confusion on Power requirements?

[JohnPunnett]

OK been reading loads & a bit confused with power requirements. I am currently putting together a project with Teensy 3.2. I have some external boards that operate from Teensy using I2C (IMU) & stepper motor drive board based on DRV8825 which is logic (3-5.25V). I have a 12V power pack & am wondering if it is preferable to operate the Teensy from 5VDC or 3.3VDC external. Does the speed of the Teensy change if you use lower volts. Also which pins do I connect the external PSU to? I still want to have capability to have laptop plugged in so I can upload new code etc. as I develop program so as I understand I need to break a connection underneath.

Any help/ clarification would be appreciated - thank you, John

 

[Arctic_Eddie]

There are numerous possibilities but here is what I would do, because I have a sheet of switching regulators, adjustable voltage at 2.2A.

Drop the 12VDC to 3V3 with a switching regulator and feed both devices. At that voltage, signal levels are not a concern, and the T32 onboard regulator is not used and hence no heat buildup. Use the 3V3 input on both devices.

Here is one of many sources for the switcher.
http://www.ebay.com/itm/DC-DC-LM2596-power-Supply-Buck-Converter-step-down-module-GM-/262136732989?hash=item3d08911d3d:g:XoYAAOSw6dNWSu3o

 

[madmattd]

You can feed either 3.6-6V to the Teensy via the Vin+Gnd pins (which will then drop that voltage to 3.3V via the Teensy's regulator), OR a regulated 3.3V to the 3.3V+Gnd pins. In either case you will want to cut the Vin-VUSB trace underneath the board so you can still upload code while the Teensy is running off the external power (note you will have to apply this external power in order to program the board again).

How you get this input voltage is up to you. Batteries of the proper voltage, switching power supplies, or even linear regulators can work (though a linear regulator from 12V to 3.3V is quite inefficient).

And no, the Teensy's speed does not vary with voltage.

 

[JohnPunnett]

Thks for quick reply - so what exactly does this refer to on Teensy page - https://www.pjrc.com/teensy/external_power.html gives impression that if you lower volts you operate at a slower speed? sorry to ask such silly questions - John

 

[JohnPunnett]

Excellent thank you - John

 

[Epyon]

Thks for quick reply - so what exactly does this refer to on Teensy page - https://www.pjrc.com/teensy/external_power.html gives impression that if you lower volts you operate at a slower speed? sorry to ask such silly questions - John

This is for the older Teensy 2.0. It is not mentioned on the page it would seem.