Powering Teensy 3.2 from external power and still have usb in with power cable in it?

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marin1454

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Hi, im building my first big project with the teensy 3.2, and i would like to have the ability to power the teensy both by USB or external power (from at power supply) - i would love to be able to have both the power supply plugged in at the same time as the usb cable, and without cutting the red wire in the usb cable.

as far as i can understand i need to place a diode between the 2 pads i need to cut, and one diode on the power input ( option 3 https://www.pjrc.com/teensy/external_power.html )

is this still the way to do it on the 3.2 if i want to preserve the usb power and use an external 5v power supply? ( as far as i can understand, if you dont cut the 2 pads, it will fry the teensy if you connect a usb and power source
 
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Cut the VUSB-VIN trace between the two pads on the underside.

Connect VUSB to VIN via Schottky diode.

Connect external 5V to VIN via Schottky diode.

Both cathodes should be attached to VIN.
 
Hi, im building my first big project with the teensy 3.2, and i would like to have the ability to power the teensy both by USB or external power (from at power supply) - i would love to be able to have both the power supply plugged in at the same time as the usb cable, and without cutting the red wire in the usb cable.

as far as i can understand i need to place a diode between the 2 pads i need to cut, and one diode on the power input ( option 3 https://www.pjrc.com/teensy/external_power.html )

is this still the way to do it on the 3.2 if i want to preserve the usb power and use an external 5v power supply? ( as far as i can understand, if you dont cut the 2 pads, it will fry the teensy if you connect a usb and power source

The schematic you were looking to is NOT teensy 3.2
For teensy3.2 you simply cut the bridge as said by constantin
no diode is required.
 
no diode is required.

Not sure I agree, but that may be due to us interpreting the intent of the OP differently.

If the idea is to be able to use the Teensy while powering it from USB and/or 5V external power, then the dual diode approach I mentioned is a proven approach.

If the OP wants to be able to use the Teensy via USB but only wants to power it externally, then simply cutting the pad should suffice. 3.9-5VDC would then have to be applied to VIN.
 
Not sure I agree, but that may be due to us interpreting the intent of the OP differently.

If the idea is to be able to use the Teensy while powering it from USB and/or 5V external power, then the dual diode approach I mentioned is a proven approach.

If the OP wants to be able to use the Teensy via USB but only wants to power it externally, then simply cutting the pad should suffice. 3.9-5VDC would then have to be applied to VIN.


yeah i want to have the option run it in 3 modes: 1 be able to code on it by usb only, 2: run power supply only 3: Usb and Power supply at the same time - so diodes it is right?
 
Diodes it is then. I tend to use Schottky's even though it's not really a requirement. After all, the on board voltage regulator will operate just fine on 4.7 or 4.3V on the input side.
 
Diodes it is then. I tend to use Schottky's even though it's not really a requirement

Constantin ...... I've been looking for a schottky diode from my local stores. But none of them has one. They were able to give me a regular rectifier diode. Will this be OK in place of the schottky?
 
Constantin ...... I've been looking for a schottky diode from my local stores. But none of them has one. They were able to give me a regular rectifier diode. Will this be OK in place of the schottky?

Regular Diodes should work just fine in this application. For me, the use of Schottky's on power buses is simply a habit now.
 
Cut the VUSB-VIN trace between the two pads on the underside.

Connect VUSB to VIN via Schottky diode.

Connect external 5V to VIN via Schottky diode.

Both cathodes should be attached to VIN.

Constantin, I did the steps you outlined for the double diode setup. However the Teensy does not run when external DC 5v is turned on. It only runs when USB cable connected. I'm using Teensy3.2. Have I done something wrong here?
 
Wow...I was fooled into thinking everything was OK running off USB after the double diode solution recommended. What I realise happening is ...now the Teensy cannot program new sketches. A message return's after uploading stating "Teensy can't order automatic rebooting. Press button to enter manual programing mode". After pressing the button, Teensy does not reapond. Teensy LED does not blink until I remove the USB cable and insert again.(The old sketch then will be running). This wasn't the behaviour before the double diode. Has the board been damaged? If yes why is the double diode working for others and it's not working for me?
 
Maybe it's not connected properly?

Usually posting photos of how you actually connected the parts can help...

Thanks Paul,
I will post picture of how I'm connecting when I get home.
Let me share my observation so far:
Contrary to my thought that my teensy was dead, I read on the teensy troubleshooting site that some USB cables are only for charging mobile phones. It turned out to be it was a phone charging USB cable I was using. Hence it was running the teensy yet couldn't program it. I changed to a cable that supports data transfer...and with all smiles the teensy is now reprogrammable. All these while
SCENARIO1
1.The strip between VIN and VUSB was cut. 2.The diode connected between VUSB -VIN. 3.Cathode on VIN pad
4.Teensy powered from USB alone
RESULT:
The USB programs and powers the Teensy.

SCENARIO2
1.The strip between VIN and VUSB cut.
2.The diode connected between VUSB -VIN.
3.Diode connected between 5V and VIn
4.USB cable removed

RESULT:
Teensy stops running
It''s obvious powering from external is not working.
I've ran out of ideas. Pls help.
 
Some high resolution pictures of the cut would help. You may also want to use a DMM to see what the resistances are for various connections. You may have cut the wrong trace.

I also would check if the diodes are arranged correctly.

This double diode approach usually works for everyone that's tried it.
 
Some high resolution pictures of the cut would help. You may also want to use a DMM to see what the resistances are for various connections. You may have cut the wrong trace.

I also would check if the diodes are arranged correctly.

This double diode approach usually works for everyone that's tried it.


So I'm back to where i left off. I soldered back the cut strip btween VUSB-VIN.
I did some health checks on the Teensy3.2 and found my board was healthy(Measured the VIn with USB power and voltage was 4.95V. Measured the 3.3V Pin. Also found it to be 3.31V)
I then loaded the blink skectch and powered via USB alone. It Run fine.
It turned out my Breadboard was the culprit why the External could not run the Teensy. I removed and reslotted at different position on same breadboard and powered the Teensy alone from a hefty 5VDC ,60A supply. I was all smiles again
I decided not to cut the strip again since the blob of solder was thick and for fear of soldering iron damaging the pads on teensy i opted for Option #2 "Cut the Red Wire" in www.pjrc.com/teensy/external_power.html
I'm all smiles again as I can now load sketches onto the Teesny with external power still connected and run it off the same external.
My next move is to play with FastLED and OctoWS2811 Libraries.

Thanks Paul & Constantin for your support. Will Let you know how things are panning out
 

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