I am working on a PCB with PIC18F26K22 which connects to a Redpine Wi-Fi module through UART.

I initially checked if PIC works with a simple LED blinking program with internal oscillator and it does. I check the same blinking with 11Mhz external oscillator + 27pf capacitor circuit and it works. As soon as I write code into the Wi-Fi module, my supply i.e. 3.3V and ground pins are getting shorted, burning up my microcontroller. This has happened on all the PCBs with this layout.

My observations/doubts(all suggestions/criticism welcome). My biggest suspect here is the PCB layout - 1. I initially doubted the external oscillator layout and removed the grounding below the crystal. I also placed the caps after the crystal after reading some posts on this forum. 2. Since the above didn't work , I checked Wifi working with the internal oscillator only ,but the burning persists. 3. Next I cut the Rx and 3.3V supply tracks on Wifi and hardwire them but still the problem persists.

I have attached my layout here. Any suggestions would be great!

Note : I have my PIC+ WiFi module hardware combination and code working on a number of other project PCBs but not this board :(enter image description here

enter image description here

  • \$\begingroup\$ I would start by removing all the traces underneath the WiFi module.. \$\endgroup\$ – m.Alin Sep 14 '15 at 8:15
  • \$\begingroup\$ Have you accidentally connected the transmit pin of the µC to the transmit pin of the Wifi module? As they work in push-pull they can short each other. You could place a series resistor in the TX and RX line to reduce the maximum current flowing, so your µC doesn't get killed, but it may degrade your maximum baudrate. \$\endgroup\$ – Arsenal Sep 14 '15 at 8:15
  • \$\begingroup\$ Traces on the bottom layer would affect the uC's functioning? My other boards work fine with traces underneath. \$\endgroup\$ – Bijlee26 Sep 14 '15 at 10:22
  • \$\begingroup\$ @Arsenal - Tx and Rx are connected alright. Just as an additional info,I have with me today new PCBs with a revised layout, my Wi-fi is creating problems while working with the external oscillator and works ok with internal Osc. I'm trying to figure out how to attach that picture here. \$\endgroup\$ – Bijlee26 Sep 14 '15 at 10:31

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