My little altimeter

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Do you see much noise from the pressure transducer bridge?
It looks to be a Motorola MPXM2202 unit that is tested with a 10V drive.
I have ran a few off 5V but worried about amplified noise.
Also running off a Lithium battery you must be using a step up regulator so you can drive the accelerometer from 5V.
Any noise issues seen from the regulator??

Nice project, good luck.
Robert
 
Do you see much noise from the pressure transducer bridge?
It looks to be a Motorola MPXM2202 unit that is tested with a 10V drive.
I have ran a few off 5V but worried about amplified noise.
Click to expand...

I was concerned about that, too, so I put a small RC on the output. Given the filter, there's very little noise, about 1-2 counts, which is the equivalent of 2.5-5 feet. I also use a differential amp built into the microcontroller, so I can effectively use all 13 bits of A/D to zoom in on the 0-35,000 foot range. clean analog ground plane probably helps too.

Also running off a Lithium battery you must be using a step up regulator so you can drive the accelerometer from 5V.
Any noise issues seen from the regulator??
Click to expand...

No, I'm just running the sensors and the microcontroller on a 3.6V linear regulator. The accel is supposed to be good down to 3.5V, and the bridge pressure transducer just divides down the input voltage, so it doesn't mind the 3.6V. I'm having fun with record attempt rockets, so the Parrot altimeter is typically packed into a small nosecone right next to a BeeLine transmitter, and there isn't even a little bit of detectable noise from that.

See here for some example data. Since then I have optimized the scaling resistors to improve the barometric altitude resolution.
 
Interesting. That table appears to be inconsistent with the data sheet. But probably it's because they put sensitivities in the table, which are only applicable at 5V. The output is ratiometric with the supply voltage, so the V/gee is lower at 3.6V.
 
Do you have the altimeters in stock now?

Also, would you mind being my secret santa :p ?
 
Do you have the altimeters in stock now?
Click to expand...

I do. I have about 25 that were all calibrated together and programmed. But I've been kind of low key about it so far, providing them to just a few rocketeers as beta testers. Although I've been testing different versions of the prototype myself for months, this is the first time that I've just handed them off to others to use, and from their feedback I've been improving the user's manual. The new feature of a single apogee deployment is one that I haven't even flight tested myself yet, and I was planning for other people to fly them some more in case there are any changes I need to make to the flight program.

So you can order now from the website, or you can wait a bit to make sure there aren't any bugs to be ironed out. At some point in the future, I think I will raise the price somewhat, or at least charge for shipping.

My near-term plans are to work with the Parrots some more, and do my own apogee deployment testing to make sure everything's right. I'm also working with the guy who makes the BeeLine transmitter so that he can make a smaller version of the transmitter with common mounting holes with the Parrot, and that will also have an arming switch, battery and screw terminals for the Parrot apogee deployment charge. The goal is that with a Parrot and the Parrot version of the BeeLine, you can have a set of record attempt electronics including a transmitter and altimeter with apogee deployment for under 15 grams, where all you need to add is the e-match (or igniter) and deployment charge.
 
When I first read this thread, I was excited that someone was making a compact & lightweight altimeter. The perfectflite model always intrigued me, and yours comes in smaller, and lighter.

However, this version has become a bit more convoluted; apogee deployment, etc.

I'm still interested in this model, and perhaps will buy one in the near future.

Though I do hope in the future you consider a no-frills, lightweight, low-cost altimeter as you mentioned at one point in this thread.

-Breeze
 
Umm... that is exactly what the parrot is...

the apogee deployment is a future, separate add-on
 
Breeze1913 said:
When I first read this thread, I was excited that someone was making a compact & lightweight altimeter. The perfectflite model always intrigued me, and yours comes in smaller, and lighter.

However, this version has become a bit more convoluted; apogee deployment, etc.

I'm still interested in this model, and perhaps will buy one in the near future.

Though I do hope in the future you consider a no-frills, lightweight, low-cost altimeter as you mentioned at one point in this thread.

-Breeze
Click to expand...

Honestly, this thing is a no frills model, relatively speaking. Setup is a breeze - there are zero wiring connections as it has an onboard battery, the deployment feature is nice, but not obtrusive, and there are not any significant problems it introduces. As for cost? For any recording accel/altimeter, $110 is not bad at all, especially not one of this size. I don't see what you are complaining about.
 
On the left is a Parrot prototype before I added the apogee deployment feature. On the right is a Parrot production unit with the bare-bones apogee deployment. :)

The differences are that I changed the 2-FET chip (tiny black part just under the buzzer at the top) with a higher-current version that had the same size, and I routed the FET outputs to the two top mounting holes, which are now plated through-holes. The other FET in the package still switches the buzzer. To use the Apogee deployment feature, you would have to wire up a separate battery, arm switch, and the ematch/ignitor in a loop that includes those two top mounting holes. What's between the mounting holes is just a switch.

And if you don't want to use the apogee deployment feature, you can just ignore it. The two mounting holes will just have a low resistance between them for about a second at apogee. If you don't add a separate battery or other power source to them, it's just like a mechanical switch flying up there that's not connected to anything.

agogee change2.jpg
 
Adrian A said:
On the left is a Parrot prototype before I added the apogee deployment feature. On the right is a Parrot production unit with the bare-bones apogee deployment. :)
Click to expand...

In recent investigations while writing software for my own altimeter, I found that I was getting a lot of analog noise from the buzzer. I tried a variety of buzzers (piezo, magenetic) and even put a buffer transistor between the microcontroler (AVR Tiny85) and the buzzer as well as a plethora of capactior values from the buzzer to ground.

I'm curious if you encountered this problem?

Glen Overby
 
Prolly ground bounce.....

Bet you have no ground plane....and a tiny trace distributing power and ground around the board....

Examine the current loop to/from the piezo and what is inside the loop.
 
overby said:
In recent investigations while writing software for my own altimeter, I found that I was getting a lot of analog noise from the buzzer. I tried a variety of buzzers (piezo, magenetic) and even put a buffer transistor between the microcontroler (AVR Tiny85) and the buzzer as well as a plethora of capactior values from the buzzer to ground.

I'm curious if you encountered this problem?

Glen Overby
Click to expand...
The old R-DAS Classic also had noise pickup from the piezo buzzer. I could minimize it by using the lower current option, however I was never sure if it was acoustical pickup on the mems sensors through the circuit board, or due to variations in the current draw from the battery changing the power supply voltage and feeding back through the system.

Bob
 
I saw some effect of the beeping in the data (though not severe), so I fixed it by turning off the beeping during the flight. When the flight recording is done (30 minutes after liftoff), the Parrot does a different sort of beep to help locate the rocket if you haven't gotten to it yet.

For your alt, if you still want to minimize the effect of the beeper on your data, rather than just working around it, here are some things that I did that might help:

Connect your analog measurement circuitry to an analog-only ground plane that should have near-zero current. Isolate the ground plane from the digital ground plane that is used by the rest of the altimeter with your layout editor (assuming you're making a printed circuit board; if not, you're probably out of luck). Connect the analog and digital ground planes at one point near your voltage regulator.

Don't power the buzzer from the same power source that you're using for your microcontroller or your sensors; just use the microcontroller output to drive a switch from a separate source.

Make sure the buzzer isn't drawing enough current to make the microcontroller or analog voltage sag.

Keep the buzzer power and return wires away from the analog measurements.
 
Adrian A said:
I saw some effect of the beeping in the data (though not severe), so I fixed it by turning off the beeping during the flight. When the flight recording is done (30 minutes after liftoff), the Parrot does a different sort of beep to help locate the rocket if you haven't gotten to it yet.
Click to expand...

I ended up doing the same thing.

Don't power the buzzer from the same power source that you're using for your microcontroller or your sensors; just use the microcontroller output to drive a switch from a separate source.
Click to expand...

I did this on the bench, and it did solve the noise problem. I have considered powering the buzzer from the ejection charge battery, but thats inconvenient.

Thanks for the comments. I'm glad I'm not the only one whose seen (fought with) this.

Glen Overby
 
Though I do hope in the future you consider a no-frills, lightweight, low-cost altimeter as you mentioned at one point in this thread.
Click to expand...

Maybe you were referring to a concept I mentioned once for a smaller altimeter that I would call the Hummingbird? I've played around with the idea of making a smaller-yet altimeter that does only altitude, with no beeper and with the battery charging and USB interface off-board. But since then I've gotten so much interesting information from accelerometer (particularly Cd) that I don't think I would want to make another altimeter without one. Also, getting the Parrots from a prototype to a real production alt was way more time and effort than I expected, so I'm not in a hurry to repeat that experience. But maybe if someone beats the Parrot's current record of 8.5 grams as-flown, I'll be motivated to make the next world's lightest altimeter. ;)

A Hummingbird altimeter probably wouldn't be cheaper, since the barometric sensor I would use for that is pretty expensive, and the separate download board combined with the altimeter would have even more parts than the Parrot.
 
But just think...

You could set MMX records too ;)
 
But just think...

You could set MMX records too
Click to expand...

I'm having fun going after the F Tripoli record first. Last night I made the "avionics bay" structure for my next attempt (which will have apogee deployment), and it came in at 1.3 grams. I'm hoping I'll get the F rocket close enough to done before tomorrow to test out the apogee deployment flying an A8-5, :rotflol: which is the largest motor I have that would put the backup motor deployment significantly after apogee. I should be able to see what happens, though, with apogee at 160 feet altitude.

If the F rocket does its job at the November NCR launch, I heard there was a G25 about to lose its competition certification...
 
Any word on DD ver. ?
Also with the battery soldered in, how long (many cycles) would it last ?

Nick
 
The battery should last for hundreds of cycles, but it depends on how hot it is allowed to get and how deeply it gets discharged. I haven't had any wearout issues so far, but then again I have tended to move pretty quickly from one prototype to the next.

The farthest I got on a dual deploy version was to do a board design, but then I found out that to add all the features and flexibility that I think should go onto a dual-deploy altimeter, the code wouldn't fit in the microcontroller I had chosen. I think there is a different hardware and software strategy that I could do, but it's a long way off, if ever. As Al Gore would say, "I have no plans" to develop that dual-deploy board. ;)

In the meantime, I had a successful first use of a Parrot as an apogee deployment altimeter this morning. I put a beeline transmitter, a Parrot, and a screw switch described on another thread into a 29mm nosecone setup that weighed 18 grams, and used it to fire a pyrodex charge using an Estes ignitor. It worked! :)

On my near-term list of things to do is to publish the parrot source code on the website so that someone could program it to be a backup main deploy, or (like I plan to do sometime) use it as a main deploy after the motor deploys the drogue. If you're willing to get rid of the beeper and do some coding, both high-current outputs would be available for deployments.
 
If DD is a while off, then perhaps you could look at including these feature in the design.

4 Pyro Outputs (1 for Burn out of booster -airstart, 1 for Apogee Detect, 2 for Dual Deploy 50ft to 600ft) The second DD would be for initiating a motor in a Lunar Lander or anything else etc.

My perfect Altimeter would be Pressure Altitude Detection, Accelerometer, 4 pyro's as above, Mini SD card storage, 25K ft +, all sampled at the same frequency 100Hz or above, and priced below 200$ or 100GBP
 
Pigmaster said:
If DD is a while off, then perhaps you could look at including these feature in the design.

4 Pyro Outputs (1 for Burn out of booster -airstart, 1 for Apogee Detect, 2 for Dual Deploy 50ft to 600ft) The second DD would be for initiating a motor in a Lunar Lander or anything else etc.

My perfect Altimeter would be Pressure Altitude Detection, Accelerometer, 4 pyro's as above, Mini SD card storage, 25K ft +, all sampled at the same frequency 100Hz or above, and priced below 200$ or 100GBP
Click to expand...

You do realize though that if you expand your price range up slightly, for 220 euros, the R-DAS tiny will do all of that and a little more except the SD card storage. It has tons of memory though, so that isn't a problem.
 
I have a new version of the user's manual posted now at www.featherweightaltimeters.com. It has information now on using the apogee deployment feature, and also has results from the calibrations and a calibration verification.

Coming soon: An Excel-based flight analysis template. It will include a computation of the Cd as a function of velocity. I'll also probably post a separate topic on that, since it's of general interest.
 
This may be a dumb question, but I have to ask. How solid is the +-70g limit on the accelerometer? Does it simply flat line at that acceleration or will it go slightly higher? And if I do go over 70G's by say another 20g's it does it permanently kill the board? I would love to use the worlds lightest altimeter in the worlds fastest 38mm rocket if it can take the 82g's I'll throw it's way :D
 
This may be a dumb question, but I have to ask. How solid is the +-70g limit on the accelerometer? Does it simply flat line at that acceleration or will it go slightly higher? And if I do go over 70G's by say another 20g's it does it permanently kill the board? I would love to use the worlds lightest altimeter in the worlds fastest 38mm rocket if it can take the 82g's I'll throw it's way
Click to expand...

It's not a dumb question at all. The A/D conversion in the microcontroller would be maxed out if the accel's analog output continued to be linear up to 105 Gs. 70 Gs is just the maximum spec value for the accel. Above that it may or may not put out a signal above the 70 G level, and it's probably no longer linear. There have been plenty of times when I have exceeded 70 Gs, particularly during deployments, with no apparent lasting effect. Generally in that situation, the accel puts out a bogus value, sometimes a negative value, but so far it's been kind of hard to tell what it should have been because those sort of G events usually don't last much longer than the 5 ms sample time. I'd be very curious to see what it does for a smooth acceleration profile that exceeds 70 Gs for part of the trip. This sounds like a great application for the Parrot.

That Medusa liftoff photo is beautiful, by the way.
 
Adrian A said:
But maybe if someone beats the Parrot's current record of 8.5 grams as-flown, I'll be motivated to make the next world's lightest altimeter. ;)
Click to expand...

What record?
My dual deployment altimeter I flew last weekend in a 18mm rocket comes in at 7.8grams "as-flown".

And in my 13mm rocket the ebay with altimeter/batteries/charge connectors and bulkheads comes to a whopping 9grams.
https://www.geocities.com/rdh82000/13mmTwoStage/index.htm

The 13mm two stage wont fly till I finish the GPS telemetry that's going in the nosecone so I can get it back :D

Robert
 
Cool. Nice little rocket.

Usually people point out the PicoAlt that requires an 8g battery in addition to the board, but you're the first I've come across to claim under 8 grams with the battery. Congratulations. Pictures? Features? Example data? What do you use for the battery?
 
Adrian A said:
Cool. Nice little rocket.

Usually people point out the PicoAlt that requires an 8g battery in addition to the board, but you're the first I've come across to claim under 8 grams with the battery. Congratulations. Pictures? Features? Example data? What do you use for the battery?
Click to expand...

But that is the beauty of it.
You are not restricted by the MFG supplied battery.
You can decided how much capacity you need to feel comfortable with.

For my last flight I used a LiPo battery for the energy density.

But the majority of fliers using deployment want to use primary cells so they dont have to worry about charging it.
Or how many charges the thing has left.
So they don't care about the couple extra grams needed.

The others, the ones not doing deployment.

Fit into two groups.
1) Cheap. Wants it under $20
2) Deep pockets. Dont care what the cost they want it.

Group 2 numbers in the hundreds at best.

Robert
 

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