Teensy 3.2 to Teensy 4.0 - no longer working

[kevinshish]

Hi, a while back I developed a simple circuit with Teensy 3.2 to control a solenoid and fan (shown in the circuit diagram). I'm now trying to make more but with the Teensy 4.0 but it immediately gets fried. I made sure to check for all the obvious problems so I added a diode and made sure the Teensy was configured for external power. Any help on what changes I could make would be greatly appreciated.

 

[PaulS]

One of the important differences between Teensy 3.2 and Teensy 4.0 is that the pins of a Teensy 3.2 are 5V tolerant. Teensy 4.0 pins are definitely not 5V tolerant.
Could it be this is at play? Looking at the schematic I would say this is not applicable though.
What exactly happens when "it immediately gets fried"?

Paul

 

[kevinshish]

One of the important differences between Teensy 3.2 and Teensy 4.0 is that the pins of a Teensy 3.2 are 5V tolerant. Teensy 4.0 pins are definitely not 5V tolerant.
Could it be this is at play? Looking at the schematic I would say this is not applicable though.
What exactly happens when "it immediately gets fried"?

Paul

As soon as I plug in the power, the light immediately turns off and it no longer shows up on ArduinoIDE

 

[kevinshish]

One of the important differences between Teensy 3.2 and Teensy 4.0 is that the pins of a Teensy 3.2 are 5V tolerant. Teensy 4.0 pins are definitely not 5V tolerant.
Could it be this is at play? Looking at the schematic I would say this is not applicable though.
What exactly happens when "it immediately gets fried"?

Paul

As a short-term solution, I'm thinking about transitioning to the ItsyBitsy 32u4

 

[PaulS]

As soon as I plug in the power, the light immediately turns off and it no longer shows up on ArduinoIDE

So when it's powered by USB only, Teensy is working fine? The display doesn't show of course.
I assume you cut these pads and placed a Schottky diode:

Can you share a photo of this placed diode?

Paul

 

[kevinshish]

So when it's powered by USB only, Teensy is working fine? The display doesn't show of course.
I assume you cut these pads and placed a Schottky diode:
View attachment 35622
Can you share a photo of this placed diode?

Paul

Yes, I cut the pads but the only diode I added is the one on the circuit diagram between the power source (5v) and the Teensy.

 

[PaulS]

I'm a bit confused: you stated "As soon as I plug in the power, the light immediately turns off and it no longer shows up on ArduinoIDE".
So did the Teensy show up in the Arduino IDE when only USB was plugged in?

Paul

 

[kevinshish]

I'm a bit confused: you stated "As soon as I plug in the power, the light immediately turns off and it no longer shows up on ArduinoIDE".
So did the Teensy show up in the Arduino IDE when only USB was plugged in?

Paul

Whoops, sorry no with just USB plugged in its not on, but with power it briefly turns on.

 

[PaulS]

the only diode I added is the one on the circuit diagram between the power source (5v) and the Teensy.

In the schematic, I only see a diode between VCC and the input of the 5V regulator? What is VCC actually? 12V?
Is the output of the regulator indeed 5V as intended?

Paul

 

[jmarsh]

Can you post a photo of how it is wired up, the schematic shows a Teensy 3.2 and no part numbers for U1/U2.

 

[PaulStoffregen]

I see a LCD on your schematic which has pin names similar to traditional small character displays, and the part number has "16x2".

The RW pin is a concern. Normally this would connected to GND for write-only (Teensy to LCD). If this pin is driven high or floats high by mistake, the 5V powered display could attempt to drive 5 volt signals onto Teensy 4.0 pins which are not 5V tolerant.

 

[Angelo]

The LCD is powered by the 5V. So its 4 data lines will get 3.3 volts signals in write mode, but put 5V signals in read mode


edit: correct, the R/W line is on GND, so LCD data lines are inputs.