I worry about how much things cost and how long they will take. Particularly after reading this excellent post on David L. Jones' EEV Blog on the economics of selling your hardware project. I want to keep below the 2.5x cost multiplier. This week I found a tool and service which helps put my worries to rest and is helping with my designs!
I look over my order on the screen again. I'm ordering two copies of my board at about $70/board. I could have spent a few hours and built these boards for a few dollars in-house. But the vias would also have wires sticking through them, and there would be no solder mask.
I will have to wait two days for the fab house to make it, then another couple of days for shipping. Is this worth it? I look at my component list, which has grown to nearly eighty components. How will I put it all together?
I was reading this fascinating account of getting a simple electronic device manufactured, from design and engineering to supply chain and distribution. I started to get worried. Everyone talks about their trials and tribulations when outsourcing their components to China - customs holdups, language barriers, holidays, counterfeits. Why do people go to all the trouble to go to China? Should I be doing this?
When I light the Tabata Timer prototype off in my apartment, I wear ear protection. I worry that the neighbors will complain. I've gone down to the sub-basement of my building to make measurements. But still, when I meet with Dave and Anthony for our Monday morning HIIT workout in Washington Square Park, I worry if it will cut through the background noise in the park - trucks, air conditioners, horns, talking, yelling - and whether people will be able to hear it even on the eighth set of burpees. How to build a loud speaker into a small, battery powered box - that can run forever?
I finally have a board without faults, lines uncrossed, chips soldered in place. The memory seems to read, at first glance. The display shows the test text. It runs through the test cycle. Cause for celebration.
But the next morning I come back and try it again. And it dies after ten seconds. Repeat. It dies in three seconds. What is going on?
The in-house printed circuit board
The rat's nest of wires taunts me as I poke the soldering iron deep into the mess, trying to add a connection. It teases me as I try to squeeze it into the project box with loose connections that I then have to dig through and find, painstakingly. It confuses me with bad solder joints.
But I am strong. I learn how to use the Eagle PCB (printed circuit board) editor, with its symbols, devices, packages, net-lists and other arcana. I untangle the rat's nest line by line, learning to love the 'ping' noise when I make a connection. I have a piece of artwork on the screen by the end. Ready to go. Now, how do I make the PCB real?
The positive rail is at 4 volts. The boost rail reads 3.54 volts, one diode drop, as I expect.
It's been a long road to this point. I checked the naked circuit for shorts between power and ground, that the capacitor was an open circuit, the inductor a short to the power line, and that the resistors were in fact 10K to ground, 820KOhm, and 15kOhm. I applied fresh flux to the pads and got a 'fresh' chip from the desiccant-sealed bag. I used a thermocouple on the chip to monitor the temperature as I soldered it in, being careful to hold the hot air nozzle a few inches from the chip for a minute to warm everything to 100C, then bringing the air gun closer and the temperature up to ~200C, removing the heat as soon as I saw the solder flow. I rechecked the connections for shorts. This is the third attempt today.