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This area documents progress towards a flight computer system for my rockets.

Ideally this system will detect the launch, sense apogee and release the parachute.
Extra functions might include data-logging, but one step at a time!

New parachute module prototype

posted 3 Sep 2016, 08:22 by Andy Lakin-Hall   [ updated 3 Sep 2016, 09:04 ]

Here is my new parachute module under construction.

The module is made from correx - two circles top and bottom, with a V inside.

I've begun to mount the circuitry inside, so here's some photos to show the wiring.


While I'm still developing the module, I need to be able to change wiring around, so for now the patch leads will stay. Once the programming is settled I can begin to replace the patch leads with more permanent connections.

The program needs to be as follows

Nunchuck Avionics

Wii Nunchuck Avionics Module program

posted 20 Aug 2016, 02:34 by Andy Lakin-Hall   [ updated 20 Aug 2016, 02:56 ]

Time for a new avionics module.

This one will be based on an Arduino and will have a servo to release the parachute, but this time will include a Wii Nunchuck to detect launch and apogee. I have an OrangePip Kona328 Arduino Uno compatible, which I am currently experimenting with.

The Wii Nunchuck contains accelerometers, which the Arduino can read to detect movement. I need to create a program that detects the sudden acceleration at launch, and then detects apogee to release the chute. It also needs to sound a recovery alarm, so I can find it when it lands in the gorse.

Here's the program...

Rechargeable Power Supply for Picaxe board

posted 19 Apr 2011, 04:08 by Andy Lakin-Hall   [ updated 19 Apr 2011, 04:21 ]

The 3 x AA battery I was using for the Picaxe board and the Optogee system was way too heavy. 

I salvaged a lighter rechargeable battery and worked out a way of mounting this so it can be charged in place, as well as switched on and off.

I included a tiny green LED, also salvaged, to indicate when the unit is switched on - and this should help show when it is discharged too.

The battery is geld in place with a zip-lock tie, which should stop it rattling about, and also allow me to swap out the batter if I need to.


posted 22 Sep 2010, 01:32 by Andy Lakin-Hall   [ updated 22 Sep 2010, 01:50 ]

Here is LS-Op1 on the launchpad.
Unfortunately, even though the optical detector works perfectly well on the bench, in the field it fails.
The problem appears to be in the way the PICAXE chip interprets the data from the comparator.
Although it seems to supply a good digital upside-down / not upside-down signal, the PICAXE will not accept this - either interpreting a high or a low all the time.
I've tried switching the PICAXE input from digital to analogue - and this gives reliable results on the bench, but outdoors it fails 3 out of 10 times - which is no good.
What I'm going to try is build a more sensitive detector array using UV-LEDs spaced further apart, and see if this will improve the quality of the signal.

Optogee PICAXE Program

posted 15 Sep 2010, 03:16 by Andy Lakin-Hall   [ updated 15 Sep 2010, 03:32 ]

Here is the updated PICAXE program for my Optogee Parachute Release system


'Optogee_Circuit version 2
'08M Board
'LED on 0
'Piezo speaker on 1
'Opto-sensor on 2
'Push button on 3
'Servo on 4
'Display input from 3 on LED

high 0
servopos 4,100 'Set the initial servo position
servo 4,70
pause 1000
sound 1,(70,20,70,20)
pause 1000

'wait for button press while flashing LED
if pin3=0 then
toggle 0
pause 50
goto press3
high 0

sound 1,(100,20,50,40)
pause 1000
low 0

for b2 = 100 to 50 step -10
sound 1,(b2,50)
pause 500
next b2
sound 1,(30,50,30,100)

'Optocheck on pin2
readadc 2,b1
if b1>100 then
low 0
sound 1,(100,20,100,20)
servo 4,190
pause 500
servo 4,70
pause 500
servo 4,190
for b2 = 1 to 120
toggle 0
pause 1000
next b2
gosub rescue
        sound 1,(100,20,100,20)
goto init
toggle 0

if pin3=1 then goto init 'Press the button to cancel
goto Optocheck2

sound 1,(100,100,50,100)
toggle 0
pause 500
if pin3 =0 then goto rescue

The code includes a firm set of the servo in initialisation, then a countdown after the ARM button is pressed, and finally a rescue alarm.

Optogee Circuit drawn in KiCad

posted 13 Sep 2010, 06:53 by Andy Lakin-Hall   [ updated 13 Sep 2010, 13:58 ]

This is the circuit for the optical comparator for the optical apogee detector, drawn using KiCad.
This produces a circuit layout too. This is the top or component assembly view.

and this is the copper side - flipped over as it would appear on the back of the PCB.

Prototype Optical Apogee Detector Pod

posted 11 Sep 2010, 13:45 by Andy Lakin-Hall   [ updated 11 Sep 2010, 13:47 ]

I've got the Optogee detector mounted up in a parachute release pod for mounting onto a water rocket body.

Optogee Prototype Sensors

posted 30 Aug 2010, 04:49 by Andy Lakin-Hall   [ updated 30 Aug 2010, 04:56 ]

This shows the Optogee sensors mounted onto a circuit board.
There are two photo-diodes, each mounted inside a short section of opaque tube from a marker pen.
These are mounted so that one points up, while the other points down.
The connector on the bottom provides power and sends the signals from the photo-diodes to the comparator on the main board.

PICAXE-18 board niggles

posted 6 Jun 2010, 13:58 by Andy Lakin-Hall   [ updated 6 Jun 2010, 13:59 ]

I finally realised that the failures I had experienced with this board were down to the Darlington driver chip.

The Darlington chip effectively filters out the pulses I need for the Servo and the Piezo sounder - which is why it seemed as if nothing was happening.
I removed the chip from it's socket and replaced it with a DIL switch array I had in my bits box. I then used the following program..

' servo on 1 and sound with movement sensor

servo 1,80
sound 0,(100,20,100,20)

if pin7=0 then action
goto start

sound 0,(50,50,100,25)

servopos 1,190
pause 4000
servopos 1,90
goto init

This gives a beep on the speaker on pin 0 and moves the servo on pin 1.
The shake sensor on pin 7 is also detected - but this is extremely sensitive; it comes to rest only when exactly horizontal, and will trigger at the slightest movement. In fact, I think this is actually too sensitive for practical rocket launch detection as the rocket will sway as it is pressurized and gets rocked by gusts of wind on the launch pad.

PICAXE-18 CHI030 Project Board

posted 30 May 2010, 14:37 by Andy Lakin-Hall   [ updated 30 May 2010, 15:12 ]

For the next development to the FC2 Flight Computer, I've got myself this CHI030 Project Board from the PICAXE people.

This uses a PICAXE-18X Microcontroller and a darlington driver IC to provide 8 digital (on/off)

The diagram on the left shows the connections for a selection of basic components. I'll be using a Servo and Piezo sounder on the output side, and a motion sensor and an Optogee circuit on the input side.

A battery pack of 3 AAA cells provides power enough for operation of all the bits.


  • Note that input 5 does not exist. This is a characteristic of the microcontroller design.
  • The connections marked 3 and 4 should not be used with the PICAXE system. These are used by the PICAXE chip as the ‘serial in’ and ‘serial out’ PC download connection.
  • The board is configured as supplied to use inputs 0 and 1 as analogue inputs. To use these inputs as digital inputs instead, or to provide a pull down resistor for the analogue potential divider, solder an appropriate resistor (e.g. 10k) into the positions marked R8 (input 0) and R7 (input 1).

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