My Teensys keep dying!

pugface

New member
Hello all! This is my first post, but I have an issue. I'm trying to drive a vacuum fluorescent display with a teensy. And I actually got that to work, and it was working for about a day and a half, before the teensy just quit working. so I took the old one out, and made some changes to the circuitry, and put a new one in, which again worked for a little bit, before also quitting.

desk vfd-desk-vfd_rev-a.png

above is the first version of the circuit. Apologies for the wire mess. Most of the bulk of wires are not important, and just go from the output pins of HV518 to the connector.

The teensy is being powered via the USB cable, and the relays are also powered by the teensy. The HV518 chip is a 32-output shift register that controls the VFD. The datasheet specified a specific power-up and power-down sequence for the chip, hence why the 5v power and 12v power are run through relays.

The ground of the external power supply and the ground of the teensy are separated, only because I wasn't sure if that would create any issues if I had them connected.

The 12V from the power supply goes into a 9v regulator, which then goes into the Vpp pin on the HV518.

The 12v also goes to a 6v regulator, which then goes into a 555 chip.
I'm using the 555 chip to make an oscillating voltage for the filament of the VFD, which was supposed to even out the brightness. It turned out that my 555 circuit really didn't do much to the display brightness, which is why i came up with this new design:

desk vfd-desk-vfd_rev-b.png

this is the current design of the circuit. I'm now using a 12v AC power supply, and just using a resistor to drop the voltage down to what I need for the filament. Then I'm using a diode rectifier and a capacitor to turn the AC into DC to input into the Vpp pin on the HV518. This circuit also worked for a bit, before the second teensy decided to quit working.

The question is: why?
I'm not completely sure, but I found out the positive wire for the coil on one of the relays was loose, and sometimes that would end up making the relay oscillate, because the relay would shake the wire every time it engaged. This in turn would make the voltage on Vin on the teensy bounce up and down from around 5v to a bit below 5v. Would this be the reason why the teensy stopped working?

There is still 3.3v present on the 3.3v pin, so the regulator supposedly should be working.

Any advice on how to keep myself from ruining another teensy would be appreciated. And if my explanation is confusing, let me know

Thank you!
 
You have no freewheel diodes across the relay coils, so high voltage transients will be generated whenever a relay is switched off, that's easily enough to blow up any CMOS device.
 
You have no freewheel diodes across the relay coils, so high voltage transients will be generated whenever a relay is switched off, that's easily enough to blow up any CMOS device.
Aha, that makes sense. Do you think it's safe to connect the ground of the rectified 12v to the ground of the teensy?
 
You have no freewheel diodes across the relay coils, so high voltage transients will be generated whenever a relay is switched off, that's easily enough to blow up any CMOS device.
Im looking for a programmer , do you know some who can build firmware for tennsy4.1 for audio ?
 
@mrneedmore: Have you looked at the Teensy Audio Tutorial <here> ?? After viewing this (& following along with your own actual hardware), it's very likely that you could do the programming yourself. Take a look, you might be surprised at how easy it can be . . .

Mark J Culross
KD5RXT
 
@mrneedmore: Have you looked at the Teensy Audio Tutorial <here> ?? After viewing this (& following along with your own actual hardware), it's very likely that you could do the programming yourself. Take a look, you might be surprised at how easy it can be . . .

Mark J Culross
KD5RXT
I need help with flyback voltage decay , a little more complicated
 
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