0

So I built an custom board based on the Atmega32u4. Schematics attached.

I managed to burn a bootloader for Pro Micro using Arduino Uno as an ISP.

The issue I have is that the board is dead when powered and to bring it to life I have to short pin1 of my crystal with VCC for a second. I discovered it by mistake..

The crystal I'm using is an Epson X1G004451000212.

Any idea why is this happening?

Circuit schematic

1

That's a Crystal Oscillator, not a crystal. Take the 22pF caps off to start.

Did you set the fuses to use an external clock source, vs a crystal with the internal oscillator driver (where the caps would be needed)?

Is the part oriented the correct way so it receives power and Gnd correctly?

Also, is it's performance any better than if you had just used a crytal?

https://support.epson.biz/td/api/doc_check.php?dl=brief_SG7050CAN&lang=en

vs these with +/- 10ppm stability (is that the same +/- 10 x 10 ^ -6 ?, which would b be better than 25 to 100 x 10 ^ -6) https://www.digikey.com/products/en/crystals-oscillators-resonators/crystals/171?k=crystal&k=&pkeyword=crystal&pv1989=0&pv183=6185&pv2150=u16MHz&pv253=19&FV=ffe000ab&quantity=0&ColumnSort=0&page=1&stock=1&pageSize=25

  • Note also that pin 1 of the oscillator is the standby pin. Shorting it is probably starting the signal. – Craig Sep 5 '18 at 18:55
  • Why should I remove the caps? According to a atmega32u4 documentation, those are required for a typical bus powered application. My fuses looks like this: lfuse: 0xff, hfuse: 0xd8, efuse: 0xcb. I didn't know that there is a difference between crystal and crystal oscillator. I'm a total electronics noob and this is my first more complex design.. – Bartosz Szymanski Sep 6 '18 at 9:15
  • ok, I educated myself and now I know the difference and I know why you suggested removing the caps..If I replace my crystal oscillator with a crystal unit (this one uk.rs-online.com/web/p/crystal-units/9047516) it should work fine? Off course I will remove the C5 and connect pads 2 & 4 of the crystal unit to ground as the documentations recommends. I will also change the caps to 10pf to match the CL of this crystal. Does it make sense? – Bartosz Szymanski Sep 6 '18 at 9:51
  • eureka! I removed the caps as suggested and it's working without the magic jump of the oscillator stby pin. I will however redesign the board as above – Bartosz Szymanski Sep 6 '18 at 10:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.