Altimeter with magnetic switch

[mlinny]

I love the idea of the cheap home built Arduino based altimeters that have been popping up on here and figured since there are few people on here that know more about electronics that I do. I took Boris' AltUno and removed the pyro output, so it is just an altimeter and nothing more, but I wanted to incorporate a magnetic on/off switch. I've attached my Eagle files and parts list and wanted to get a opinion as to if it will work. Based on what I've read it seems like it should and I have parts on order to test it out. If anyone wants to give their thoughts that would be great.

View attachment 147736

 

[bdureau]

I love the idea of the cheap home built Arduino based altimeters that have been popping up on here and figured since there are few people on here that know more about electronics that I do. I took Boris' AltUno and removed the pyro output, so it is just an altimeter and nothing more, but I wanted to incorporate a magnetic on/off switch. I've attached my Eagle files and parts list and wanted to get a opinion as to if it will work. Based on what I've read it seems like it should and I have parts on order to test it out. If anyone wants to give their thoughts that would be great.

View attachment 147736

Cool I am glad that you got inspired by my stuff. I will take a look and get back to you

 

[bdureau]

I love the idea of the cheap home built Arduino based altimeters that have been popping up on here and figured since there are few people on here that know more about electronics that I do. I took Boris' AltUno and removed the pyro output, so it is just an altimeter and nothing more, but I wanted to incorporate a magnetic on/off switch. I've attached my Eagle files and parts list and wanted to get a opinion as to if it will work. Based on what I've read it seems like it should and I have parts on order to test it out. If anyone wants to give their thoughts that would be great.

View attachment 147736

Could you also post your code

 

[mlinny]

I don't have code yet, but was planning on just scrubbing the pyro output from your AltUno code. If I have a chance today I'll try working on the code.

I mainly wanted thoughts on if the hall effect sensor triggering the mosfet to connect the rest of the circuit to ground would work. If so, it would be a simple way to add switch when there isn't much room.

 

[mlinny]

The hall effect sensor turns the circuit on when the battery is first plugged in, but in my initial tests it seems to work. Need to breadboard the entire circuit and built a vaccuum test chamber to do a full test.

I've worked on some code. Right now it is for my Uno which is easy to test with and will need to be paired down a little to fit the ATTINY85. Using the smaller wire and bmp085 sensor libraries hopefully will do the trick.

View attachment 148955

 

[bdureau]

I see that you are using the bmp180 sensor. This is what I am planing on using with the CMS version of the altimeters
OK so are you planning on switching on the altimeter when the rocket leave the pad?
If it is the case it will not work because the altimeter needs some time to intialise the site alititude

 

[mlinny]

Here is the order of how I see things happening : 1. Plug battery into altimeter. 2. Turn off altimeter. 3. Close altimeter bay. 4. Prep for launch. 5. Turn on altimeter once it is verticle on the pad. ---- Start of program ---- 6. Altimeter goes through its setup routine including opening communication with the barometer module, setting up the Kalman filter, and taking initial altitude readings. ---- Start of loop ---- 7. Take altitude reading. Repeat each time through loop. 8. Beep previous altitude stored in EEPROM 3 times. On first time though loop only. 9. Detect launch. Only if altitude is below minimum altitude. 10. Beep all good ready to launch beep. Will stop once launch is detected. 11. Compare current altitude with previous altitude to detected apogee. Stop compare once apogee is determined. 12. Once apogee is reached define apogee altitude, convert altitude to feet, and stop comparing altitudes. 13. Convert altitude to separate digits and write them to EEPROM. Do once. 14. Beep out altitude. Repeat until altimeter is turned off.

 

[mlinny]

Sorry for the formatting, I'm posting on my phone, else I'd have wait until tonight.

The BMP180 is smaller, so that is why I chose it over the BMP085. The library for the BMP085 should work for the BMP180 from what I've seen.

The altimeter would be powered up once vertical on the pad.

 

[H_Rocket]

I've gone on record about this before (As someone who spent years designing safety circuits). I Really think the idea of an active device in a safety loop is a truly bad idea. You cannot predict how it will fail and even worse could, IMHO, arm or disarm it accidentally without being aware of it. PAssive components should be used in this application.

My $0.02 and of course, YMMV