Trouble getting my impee to work, keeps reading sha chip

So after the hacky impee i designed my own very simple impee : linear 5 V tot 3.3 V regulator, 1 x regulator cap, 2 x 100 nF bypass caps, 100k pullup resistor for the ATSHA204 and some connectors.

The imp won’t boot. No flashing lights at all. On a scope i can the imp reading from the sha chip (the pulses have sharp edges) and the sha chip responding (the pulses have some RC time). The pulses and the shape of the pulses look the same as those on the working prototype. The SHA chip is from the same batch and the same imp will work on another impee.

I’have run out of good ideas for now. Any hints and tips on what else i can debug or tweak ?

This is the freshly baked board, it still needs some fixing.

The fact it keeps reading it is unusual, implying that the card is being reset (generally, it only reads at boot time and never again).

Have you looked at the 3.3v on the scope to see if it’s stable? It’s possible that our power supply is browning out when the imp turns the radio on. Judging by the photo of your board, there’s no capacitor on the LDO input which is unusual - you really ought to have a bulk cap there otherwise the inductance of the wires going to the board will cause problems for you.

Thanks Hugo, good catch !

The board is indeed suffering from a nasty brownout.

The non-design of the power supply was done on the basis of SMD parts i had lying around from another project. The through hole proto-prototype was built with beefier parts by accident.

Thanks again !