On a Monday morning, a 14 year old 9th grader in Irving, Texas brought a homemade clock to school. Ahmed Mohamed was hoping to impress his teachers. Instead, he was arrested. One of his teachers thought he had constructed a hoax bomb, the school principal called the police, and the police took the kid away in handcuffs. Whether you believe this story is about racial profiling or mindless zero-tolerance policies, it is clear that bright, motivated young people should be nurtured, not stepped on. The outpouring of support from all parts of the country has been enormous.
Cool clock, Ahmed. Want to bring it to the White House? We should inspire more kids like you to like science. It’s what makes America great.
— President Obama (@POTUS) September 16, 2015
On Wednesday night, I built my own hacked-up looking clock.
Let’s take a look at Ahmed’s clock.
This looks pretty straightforward. There is a display screwed to one side of this case and the sprawling guts of a digital alarm clock resting below it. We can see a transformer, a 9v battery connector, the main circuit board, and a small board containing the controls for the clock. On the main board, there’s clearly one big chip in the middle (on the other side of the board), and one whole side of its pins go directly to drive the LED display. That chip is probably an LM8560.
As it happens, I had the guts of a similar clock sitting in a box, waiting to be made whole again. Its shell had all but disintegrated from years of abuse, but I couldn’t bear to throw out a functioning (and useful!) circuit. I had always hoped to build a handsome wooden enclosure for it, with brass fittings and fancy buttons. I didn’t quite get there.
Two years ago, when I disassembled this clock, I also did my future self an enormous favor by fully documenting the wiring of the clock’s controls.
With this as my guide, it was easy to map the wires coming out of the circuit board to switches and buttons on the outside of my enclosure. I had a bunch of nice Radio Shack switches laying around, so I had no trouble implementing the full suite of controls from the original clock:
- Set time/set alarm
- Increment hour
- Increment minute
- Alarm volume high/low
- Dim high/low
- Alarm on/off
As it happens, two-years-ago me mapped the dimmer switch incorrectly. As a result, my display is always half-dimmed. This doesn’t bother me, but will be trivial to fix.
Check out my super-professional bubble wrap strain relief.
The clock works great. The dimmer doesn’t quite work, but all of the other features are perfect. We have a different solution in the bedroom now, so I’ll have to come up with another use for my revivified alarm clock. Maybe I’ll keep it at the office.
Any circuit can look like a bomb, if that’s how you choose to see it, but building (ok, assembling) a clock is not a crime. It’s not a crime for me, and it’s not a crime for a 14 year old Sudanese high school student. #IStandWithAhmed