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This is basically the same altimeter as the Basic Atom altimeter I built earlier, but I saw the need for a smaller unit. The only real difference between the two is that the small altimeter only has 2 pyro channels, and is of course, smaller. At 1" wide it should fit in pretty much any EX rocket a person would want to fly. Not a miniature altimeter by any means, it's still 4.5" long. But it is something a person with limited electronics skills should be able to solder up pretty quickly.
Here's the altimeter next to a quarter for size reference.
1" x 4.5" Single Sided Copper Clad Board
Honeywell Pressure Sensor: ASDX 015A24R
Basic Atom 28B Interpreter Chip
1) 28 Pin IC Socket
PCB Piezo Speaker
L7805CV 5 volt Regulator
20 MHz Resonator Chip
10 uF Electrolytic Capacitor
.22 uF Capacitor
2) IRF 510L Transistors
1 Meg. Ohm Resistor
2) 3 K Ohm Resistors
5) 10 K Ohm Resistors
3) 2 Position .1" Pitch Terminal Blocks
Orange lines are resistors, green lines capacitors, yellow line the resonator, purple lines are jumper wires.
Click Here for the full sized PCB image for printing with a laser printer.
Click Here for the source code for the Basic Atom 28B chip.
Here's an image showing 3 stages of making the PCB. Far left is after using a hot iron to transfer the design to the copper clad board. In the middle the board has been etched with ferric chloride. On the right the board has been drilled, then the toner cleaned off with acetone.
Here is another variation on the small altimeter. In this version I added jumper pins to vary the mach delay by the user in the field.
Click Here for the PCB image for printing.
Click Here for the Basic Atom source code.
You'll need to pick up some header connectors to use with jumpers. I bought some breakaway headers that can be snapped off to as many positions as you need, Digi Key part A34256-40-ND. The jumpers blocks I salvaged off old computer boards, if you can't salvage them, you'll need to order them as well.
In this picture you see the mach delay jumpers to the right of Atom 28B chip. From the bottom the first jumper adds 5 seconds of delay, the second from the bottom adds 10 seconds, the third 20 seconds and the top jumper adds 40 seconds. The mach delay is cumulative in that you add together the delay from each jumper inserted. If you jumped the 20 second pins and the 5 second pins, you would have a total mach delay of 25 seconds. So you can add mach delay from 5 seconds to 75 seconds, in 5 second increments.
I would advise using caution with the mach delay. If you add so much delay that apogee occurs before the mach delay runs out, the altimeter won't detect apogee. That shouldn't be a problem on any nominal flight as the mach delay should expire well before apogee. I'll see if I can work on the code to throw in emergency deploy code for unexpected flight events.