Solenoids...and near space...

[Jon_]

Hi All,

I am a local scout leader and our senior scouts are trying to assemble a weather balloon to fly up to near space, hopefully taking lots of pictures, and then come back down to collect.

We are already thinking of adding simple picaxe circuit to take temperature measurements but we also want it to trigger the camera. One way of doing this would be using a small solenoid to push the camera button, however, I cannot seem to find any small 5v solenoids anywhere!! We have no budget so it is beg, borrow or ask nicely ;-)

So i was wondering whether anyone on here knows of where I can find some small 5v solenoids...preferably a push solenoid...

many thanks!

 

[nick12ab]

Here. There's also one at techsupplies but it's "not currently available" like it's been since I first used the site.

You could make a DIY one using a rod or bar magnet and a coil of wire.

Why can't you hack the camera?

 

[Jon_]

We could hack the camera, just not sure how i would go about doing it! At least if it is kept whole i know it works!

 

[nick12ab]

We could hack the camera, just not sure how i would go about doing it! At least if it is kept whole i know it works!

The most popular way to do it on this forum appears to be using an optocoupler in parallel with the switch to short it out. Of course you could also use a direct connection to the PICAXE.

 

[Jon_]

I will have to do some research on this as I would prefer to keep it solid state. Thanks!!!

 

[eclectic]

I will have to do some research on this as I would prefer to keep it solid state. Thanks!!!

I think it would help if you specified the camera.
Then, folks may be able to offer further dvice.

e

 

[Paix]

I will have to do some research on this as I would prefer to keep it solid state. Thanks!!!

So that would rule out the solenoid then I guess that payload weight is likely to be an issue and a solenoid weighs in at a lot more than a 4N25 optocoupler.

 

[srnet]

I am a local scout leader and our senior scouts

Interesting, conventional Senior Scouts in the UK ceased to exist in 1968. So I presume BP Scouts ?

we also want it to trigger the camera

Use a compact Cannon camera with CHDK, job done, nothing else comes even close to flexibility and function. Really dont waste your time with anything else.

Most of the compact cannons support CHDK, so you can control them with a single PICAXE pin via the cameras USB port, all you need is a USB cable.

Its then easy enough (with Cannon CHDK) to make the camera take one shot or several, start a video, zoom in, zoom out, bracket exposure, etc.

 

[IronJungle]

I would not use a mechanical solenoid. If you are successful your rig is going to get EXTREMELY cold at those altitudes. Even with the heat packs that wil be required to ride on board you probably wil not be able to keep a solenoid working. I 'second' the solid state suggestion above.

Here is a link to a camera hack I did using the TI MSP430. It would be easier with a PICAXE and I certainly would recommend a higher quality camera, but this concept could be a good test bed for the project. Maybe it will help. See: http://ijprojects.blogspot.com/2011/08/walk-through-vistaquest-vq1005.html

 

[KeithRB]

When you say USB cable and PicAxe in one breath, I don't see how it can be easy. You would have to implement USB host functions in the PicAxe, no?

 

[srnet]

You would have to implement USB host functions in the PicAxe, no?

Indeed no.

Its all done with timed pulses applied to the USB power connections, nothing to do with USB host functions at all.

http://www.picaxeforum.co.uk/showthread.php?20513-Canon-Camera-Remote-Control-Interface-for-PICAXE-08M2

Mind you for the application the OP has in mind, you can forget the electronics all together, just run CHDK on the Cannon and use a script that the camera runs and takes a picture every so often.

 

[MFB]

You might also consider using one of these really low weight/cost video cameras...http://chucklohr.com/808/.

Their operation is controlled by sequencing two push buttons, but I have been able to automated this with an 08M driving transistors across these contacts. This arrangement would allow the video recording to be started and stopped a number of times during the flight.

 

[srnet]

And if you want to find your downed balloon you may want to consider the use of a GPS Locator beacon I am working on, see enclosed PDF. It uses the same code as published here;

http://www.picaxeforum.co.uk/showthread.php?21093-PICAXE-GPS-Locator-Beacon-With-Distance-and-Direction-Calculation

But this newer hardware is a fair bit easier to assemble and has options for a plug in GPS, serial LCD and Openlog logger.

It can transmit at up to 100mW and in a space type application you should hear the Morse beacon at a range of circa 2000km using a handheld UHF transceiver and modest yagi. Not sure yet, but by adding a UHF preamp you should hopefully be able to decode the Morse audio using a PC Soundcard at a range of 500-1000km. How far the data telemetry will work (with a pair of devices) I am again not fully sure but ground based line of sights tests using simple 1/4 wave antennas indicate it should be 40km or so.

And when the balloon is down, the module transmits a series of beacon tones that will allow you to retrieve your 'lost' balloon.

There is also a module that is half the size, with the same capability, but that needs to be assembled with SMT components.

 

[tony_g]

would a small inexpensive rc micro servo be a good alternative?
you could have the picaxe program set to activate the camera every so often in between running its other tasks on its way up
as budget is an issue maybe one of the scout members has a family member that enjoys rc modelling and possibly has one lying around they could donate

 

[srnet]

would a small inexpensive rc micro servo be a good alternative

You can do, that is the 'normal' method of triggering the shutter for those lesser cameras that wont run CHDK.

Be careful mind, not too powerful a servo, if it goes wrong you can damage the camera button.

Not sure how well the servos work in a near space environment though.

 

[AllyCat]

we also want it to trigger the camera.

Hi Jon,

As in the majority of threads on this forum, we really need facts!. Have you chosen a camera yet, what is it, how much does it weigh? Have you quantified the "cost" of any specific weight, for example the price of helium?

The majority of digital cameras have a "two stage" shutter button, firstly to focus and set the exposure, then a harder/further press to take the picture(s). A tiny geared motor is likely to do this better than a solenoid, maybe a mobile phone "vibrator" driving a screw thread.

But you/they probably need to avoid ANY mechanical operations at all (think clouds, condensation, sub-zero temperatures, ice, etc.) so a very basic (and light) fixed focus camera with an electrical connection to the shutter switch is IMHO likely to be a better solution. As a test, try putting the camera assembly in a home freezer and see if it takes pictures after an hour or so.

Cheers, Alan.

 

[srnet]

The majority of digital cameras have a "two stage" shutter button, firstly to focus and set the exposure, then a harder/further press to take the picture(s). A tiny geared motor is likely to do this better than a solenoid, maybe a mobile phone "vibrator" driving a screw thread

With every digital camera I have come across, just press the shutter button all the way and it does it all.

Sure you can press the shutter half way and see (on the screen) what its focusing on or setting exposure on, then decide what you want to do next etc, but for remote operation who cares, just press the button.

 

[erco]

Solenoids almost always disappoint in terms of force, travel, and power consumed. You're much better off using a small servo. Even a $3 9-gram servo generates far more usable force over a longer distance and uses less power compared to a solenoid. It won't require any external hardware (switching transistor, etc) and has the advantage that it is easily possible to adjust travel for pushing the shutter button halfway if desired.

 

[Jon_]

Ok, sorry I haven't replied in a while, i am not deliberately ignoring you all!

Interesting, conventional Senior Scouts in the UK ceased to exist in 1968. So I presume BP Scouts ?

Indeed, I am part of the BP scouts ;-) My particular troop was founded in 1993. We have just started a new website if you are interested in the group: http://1stblackwatervalleyscouts.co.uk/

As in the majority of threads on this forum, we really need facts!. Have you chosen a camera yet, what is it, how much does it weigh? Have you quantified the "cost" of any specific weight, for example the price of helium?

The project is still in preliminary stages of costing. Another leader has an old digital camera they are willing to donate to the cause but has not yet got back to me of what model it is. The weight of the module (that would contain everything, GPS, camera etc) we are looking at 600g. We already have a weather balloon capable of lifting that weight and the helium would be cheaper. We already have a few sources of helium at hopefully cheap prices, again we are still negotiating this ;-)

you may want to consider the use of a GPS Locator beacon I am working on,

Thanks, i will definitely look into this.

We are currently facing issues with GPS tracking and radio comms, the expense of radio transmitter units is not too bad but the equipment to receive is much more expensive!!

I know this post adds little extra info, I will add more as I get it, but I just wanted to show that I was not rejecting all yours ideas and questions ;-) thanks for all the help so far!

 

[IronJungle]

For GPS tracking your easiest solution (maybe the cheapest) is to just use a smart phone with one of the several available for free GPS tracking apps. As long as you are in range of cell phone coverage the long/lat can be tracked on the groung via the web. Problem solved.

 

[srnet]

We are currently facing issues with GPS tracking and radio comms, the expense of radio transmitter units is not too bad but the equipment to receive is much more expensive!!

It does depend on what you call expensive.

Whilst there are numerous TX & RX pairs of data modules, the receiver parts do tend to be relativity deaf, although even then the Hope Modules I have been using (about £10) are capable of circa 10kM line of sight, such as from a ground station to a balloon, at the 'license exempt' limit of 10mW, and that with simple 1/4 wave wires at either end.

If the frequency you use is in the 434Mhz region, where one of the 'license exempt' bands is, there are quite a few options that you can take on the cheap, to improve range. 434Mhz is in the region of the amateur 70cm band, so there is a lot of DIY kit and plans for antennas and stuff.

For instance, you can improve reception range (at the ground station) considerably by using a high gain antenna such as a yagi. Sure you can by them, but you can also make them with little more than a wooden pole and some stiff wire.

There are a few UHF preamps available that should improve reception considerably too, I just bought a kit for £20, waiting for the box to arrive.

Morse is easy to transmit and easy to decode. There are UHF\70cm transceivers (designed for Amateur use) available for around £25, these are very much more sensitive than the average data receiver module. So transmit in Morse, and feed the audio into a PC or Laptop with soundcard and decode the Morse with that (the software is free).

 

[srnet]

Indeed, I am part of the BP scouts ;-) My particular troop was founded in 1993. We have just started a new website if you are interested in the group: http://1stblackwatervalleyscouts.co.uk/

No particular interest, its just that I recognised what Senior Scouts used to be.

I was a Boy Scout when they changed across to Scouts, although the media and general public dont seem to have realised that 'conventional' Boy Scouts ceased to exist over 40 years ago.

And I recall vividly the Senior Scouts in my troop in 1968, I still know some of them as they became local Scout Leaders.

I am still in Scouts, although not as a leader these days, I am an activity assessor for Hillwalking and Rock Climbing.

 

[Jon_]

Whilst there are numerous TX & RX pairs of data modules, the receiver parts do tend to be relativity deaf, although even then the Hope Modules I have been using (about £10) are capable of circa 10kM line of sight, such as from a ground station to a balloon, at the 'license exempt' limit of 10mW, and that with simple 1/4 wave wires at either end

I have to confess I am no radio expert...are you talking about these types of modules:

http://uk.rs-online.com/web/p/radio-telemetry-data-modules/7312782/

Searching online there are alot of threads from people new to radio technology finding it very difficult to understand how to use them....which concerns me....

 

[eclectic]

I have to confess I am no radio expert...are you talking about these types of modules:

http://uk.rs-online.com/web/p/radio-telemetry-data-modules/7312782/

Searching online there are alot of threads from people new to radio technology finding it very difficult to understand how to use them....which concerns me....

Just a thought.
If you're going to buy some Picaxe kit, then
these:

http://www.techsupplies.co.uk/epages/Store.sf/en_GB/?ObjectPath=/Shops/Store.TechSupplies/Products/AXE213
http://www.techsupplies.co.uk/epages/Store.sf/en_GB/?ObjectPath=/Shops/Store.TechSupplies/Products/RFA001

will come with a mass of expert support; This Forum.

e

 

[srnet]

I have to confess I am no radio expert...are you talking about these types of modules:
http://uk.rs-online.com/web/p/radio-...dules/7312782/

Yes, that sort of thing. Hope also do a more powerful transceiver, the RFM22.

And as mentioned by eclectic Rev Ed sell and support their own.

Myself I would be wary of the AM modules, for your application where extended distance is essential, if you stick to FM modules you have the option of using cheap but highly sensitive UHF transceivers at the receiving end, so if you use the transmitter module to send Morse audio that will extend the useable range of the transmitter considerably.

 

[premelec]

On the actuator - best use a small servo or DC motor & spring- solenoids are pretty low force without big ampere turns.. [as previously mentioned - I agree ] - many cameras have electronic shutter control [not my Canon though..] so no actuator would be required on one of those...

 

[srnet]

Searching online there are a lot of threads from people new to radio technology finding it very difficult to understand how to use them....which concerns me

Here we go, these two devices use an RFM22 and PICAXE 28X2, up to 100mW output, cover all frequencies from 240Mhz to 930Mhz. Data telemetry or Morse. Connections for serial LCD, GPS and Openlog logger (the small red PCB). Spare IO pins on the pin header.

The bigger one is easier to make, can be built using wired components, suitable for a baloon perhaps. The smaller uses 1206 SMT parts to keep the size down.

For an idea of the size, the batteries are AAAs

 

[Jon_]

what sort of antenna should be used on the transmitter?

 

[eclectic]

what sort of antenna should be used on the transmitter?

A bit of background info:

http://ukhas.org.uk/guides:tracking_guide




e

 

[eclectic]

And further, how about the RSGB Foundation course
for some of your scouts?

http://www.rsgb.org/clubsandtraining/

Could be possible in less than a month.

e

 

[srnet]

what sort of antenna should be used on the transmitter?

Non directional, as you dont know which way the balloon is pointing, I guess. So a vertical of some type, a simple 1/4 wave stiff wire is as good as any (approx 17cm at 434Mhz) , although there are other variants which give a bit more gain. Its important that the antennas are matched (tuned) to the transmitter and receiver, this can make a fair bit of difference, basically you adjust the length. Its not that difficult with the Hope modules, if you use a pair. The receiver part has a RSSI (received signal strength indicator) register, so with one acting as a receiver you adjust the length of the antenna on the transmitter for maximum RSSI value.