About the new single sided PCB

A project log for Brightenmacher

A biodegradable flashlight, build with recycled laptop batteries that you can repair yourself.

Peter FröhlichPeter Fröhlich 04/25/2017 at 19:260 Comments

A lot of work went into this, mostly though in the background on my custom part library that has been tidied up, a lot.

The schematic was slightly overhauled and changed a bit, the PG output of the MCP73833 is no longer used, i wanted to route it to the AVR but could not settle on a solution i liked.

The PG is a pseudo open drain output, that made it a bit harder to wire it to the AVR without adding more parts or using board space. I am sure someone else will point out a solution i missed straight away though.

So, only the presence of the USB supply voltage is monitored again and the blue LED of the charger status RGB led is connected to the AVR since i do not want it to light all the time.

That would swamp out the Red and Green LEDs.

A solder jumper has been added to disable the battery NTC in case it is not present, otherwise the charger will not work.

The system status LED has been moved between the switches, the idea is to print the center switch in transparent PLA, that should make for a nice aesthetic and will give me more room for the actual button caps.

Besides that, not much has been changed just moved around a bit:

All components have been moved to the top side and all connections to the board to the bottom, the switches have been changed to a THT footprint.

This has been done for two reasons, to locate them on the board and have a known reference to the CAD parts, SMD switches may be a bit crooked on the pads.

But mostly due to the reason that i could not find suitable SMD switches.

These are Omron switches with 500 gram activation force, about twice as much as the usual tactile switch.

Together with a switch lever design that is a bit better thought out i hope to achieve the desired tactile feedback from the switches with a well defined travel and klick.

A bit of silkscreen should help me to wire if up correctly, i might change around a bit of this but i think i am done.

Although it does look a bit boring, the text is a bit small but after checking what it looks like printed and after a few test prints i decided that it is at the lower limit of what is achievable.

But i suspect the print may fail and not be readable, i tried to keep the isolation to pads a bit bigger in case the board house misalignes the silkscreen layer, which seems to happen from time to time.

All silkscreen has been moved around to keep it away from vias as much as possible.