Apple II

Spot The Design Error

June 15, 2018 Big Mess o' Wires

A prototype for the latest Star Ring. Q1, Q2, and Q3 use this N-channel MOSFET. The circuit runs from a 3V battery. When one of the transistors is turned on, the six red/green LEDs in the associated row can be turned on or off using six microcontroller outputs. At

Apple II

Atmel ICE Wiring Horror

June 14, 2018 Big Mess o' Wires

The Atmel ICE programmer/debugger has its SWD connector pins reversed from the standard ARM Cortex debug connector. Arghh… why? It’s the same physical connector (5×2 0.05 inch polarized male), but the pins are rotated 180 degrees from the standard, as if the cable were plugged in backwards. Incredibly, it

Apple II

Where Did All The Watts Go?

June 10, 2018 Big Mess o' Wires

How efficient is a typical 5V AC-to-DC power supply? I’m digging through my box of assorted power supplies from past projects, looking for something appropriate for a large LED matrix, and noticed the one pictured above. 110V 0.8A input – that’s 88 watts. 5V 4A output – that’s 20

Apple II

Limiting SD Card Inrush Current

June 6, 2018 Big Mess o' Wires

I’m experimenting with methods to limit the inrush current when an SD card is inserted, and beginning to wonder whether my solutions are worse than nothing.

When an SD card is inserted into a board that’s already powered on, a large amount of current will flow briefly, as the

Apple II

LED PWM Without Resistors

June 1, 2018 Big Mess o' Wires

I’ve been working on version 3 of Star Ring, my fun but useless circular LED blinker, and I had an idea. Do I really need current-limiting resistors for the LEDs? Or can I effectively control the LED current using PWM?

Normally a resistor is always needed in series with an

Apple II

Raspberry Pi GPIO Programming in C

May 26, 2018 Big Mess o' Wires

The Raspberry Pi’s 40-pin GPIO connector often gets overlooked. Typical Pi projects use the hardware as a very small desktop PC (RetroPie, Pi-hole, media center, print server, etc), and don’t make any use of general-purpose IO pins. That’s too bad, because with a little bit of work, the Raspberry