Wednesday, June 26, 2019

Sunbeam Coffee Maker Teardown

The bad Kenyan grid has struck again. There is very little built in surge protection in the system, so all appliances plugged to the wall end up with in-house surge protectors. This time the victim was my beloved coffee machine which had served us well for more than a year.

So I decided to take it home and spend some quality time with Pascal tearing it down. He is always curious about stuff and what is inside, so the Coffee machine is a complex beast capable of keeping him and myself occupied for hours on end. First we took of the top and looked at the heater and the electromechanical assembly controlling the hot-water head and frother was exposed. Also was exposed the heating tank with dual heating elements and a thermistor (I am assuming a thermistor rather than a thermocouple).

When we took the back plate off we found the main controller board. There is to obvious transformer in the set-up so I assume to whole power supply is cap-drop. There is a giant heat-sink attached to a 3-pin device which I assume is a triac or SCR for controlling the heating elements.

The bottom-left corner has a water pump with its own switching mechanism driven by relatively thin signal-wires from the main board.

There are some more interesting details on the main processor board including thick high current traces driven by the silicon switch with exposed copper and extra solder on top to increase thickness and provide a lower current path.

The main CPU is TQFP packaged micro-controller which is covered by the conformal coating the entire PCB is covered in. A macro image on twitter helped establish the lineage of the processor. It is a chinese 8051 variant with the datasheet here. Any help in translating it will be highly appreciated. But most of the schematic is legible.

Next up will be powering on the processor with a suitable 3.3v supply and examining the analog and digital buses. As well as powering on the whole thing to see why it turns of immediately on start. If the machine is unfixable I am planning to scavenge the thermistors, heating elements etc. to build a reflow mechanism.

All the water circulation mechanism is really interesting as well and can possibly be shoe-horned into a water cooler for a 3D printing system.

Saturday, June 22, 2019

Nairobi 2nd OSHW meetup

After a many month hiatus we finally put together the 2nd Nairobi Open-source hardware meetup. This time we were at the Tav Irish Pub near Nairobi Garage on Waiyaki way. The pub was chosen due to proximility to Nairobi garage and possible use of that venue. As it turned out none of us were memebers paying the $60 per-month fee so we ended up co-opting the pub in Chicago 3H fashion.
PCB Lineup
PCB Lineup
I had collected PCB's over the last few month from Aisler, OSHPark and PCBWay all shipped to Kenya from Germany, US and China respectively. So we lined up to try various soldering techniques on 0603 Jellybeans and some 20pin TSSOP IC's.
Soldering demo
Soldering Demo
The techniques we we tried were the tack, finish and reflow one using the iron and an experimental one with paste and dry-iron I had picked up recently. I didn't have a temperature profile controller for the dry-iron method. So we were just going to wing it by the eye.
Part Placement
Part Placement
We pasted up the boards using screwdrivers and tweezers. Started the reflow till the parts settled. Then simply turned off the iron. I am sourcing a K-Type thermocouple and SSR from KTechnics to get a better handle on this for next time. However the dry-iron does reach sufficient temperature for leaded solder reflow.
Dry iron reflow
Dry iron reflow
By the end of the session we had assembled x2 CS5464 Breakouts. Next step from here will be suitable MicroPython and Arduino drivers to ensure these things actually work. We had a lot of fun over the meetup and I hope to continue having these sessions. Next time one of the participants has promised to bring his Weighbridge Automation and IoT set-up.
Scavenging Coffee Machine
Scavenging a Coffee Machine
Following the meetup I have been hunting for accessories to make the dry-iron reflow less of a fire hazard and more controllable. (Un)fortunately the coffee machine at work has been fried by the spikes prevalent in the grid in Kenya (especially during the rainy season), so I have a spare K-type thermocouple I can work into the build. I have also co-opted a tissue holder we had on our dining table to stabilize the inverted iron during reflow.
A stand of opportunity
Stand of opportunity
Onwards to the next Meetup.