Launch Detection (almost)

Discussion on ground control/GSE and recovery equipment. This includes launch pads, triggers, chutes, streamers etc. Includes other items such as simulation and other computer software, etc.

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OverTheTop
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Re: Launch Detection (almost)

Postby OverTheTop » Thu Nov 12, 2015 8:02 am

P.S. Strud, your avatar sounds like a conversation I frequently have with myself.


Just search for "monty python buy an argument" :D
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Re: Launch Detection (almost)

Postby lorstin » Fri Nov 13, 2015 6:14 am

I've been to the cheese shop next door to that place OTT, but all I bought was a dead parrot, no it wasn't................
caveat emptor :?

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Re: Launch Detection (almost)

Postby lorstin » Fri Nov 13, 2015 10:34 am

On a more serious note, the RF units that you mentioned Troy are available as a cheap Chinese copy on ebay (circa $6 for both the tx & rx units). Have you had any experience with these? or should I steer clear of them?
I've noticed that Adafruit & Core-Electronics are out of stock.
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Re: Launch Detection (almost)

Postby rocket_troy » Fri Nov 13, 2015 12:18 pm

lorstin wrote:On a more serious note, the RF units that you mentioned Troy are available as a cheap Chinese copy on ebay (circa $6 for both the tx & rx units). Have you had any experience with these? or should I steer clear of them?
I've noticed that Adafruit & Core-Electronics are out of stock.

Go for it. The only issue I've had with Chinese electronic modules from Ebay is the consistent void of any accompanying instructions or manuals. Other than that, they generally work. Because these are quite simple to interface, you shouldn't need much instruction [fingers crossed]

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Re: Launch Detection (almost)

Postby lorstin » Tue Nov 24, 2015 3:33 pm

I know what you mean about the lack of instructions when buying Chinese modules from ebay, however I see this as a blessing in disguise - saves alot of confusion.
Anyway I bit the bullet and bought one, complete with retro styling! At $4.39 for tx and rx I don't think you can go wrong.
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Re: Launch Detection (almost)

Postby Lister » Tue Nov 24, 2015 4:28 pm

I have used them.. pretty good for the price

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Re: Launch Detection (almost)

Postby lorstin » Wed Dec 30, 2015 7:29 am

I noticed after I ordered the above RF unit that the picture did not show an antenna on the circuit board. My first thought that it was just a photo of a dodgey item that had been overlooked, no big deal anyway it's only a lump of wire. The item arrived and was minus the antenna. Does anyone know the formula to calculate the length of wire (433 Mhz) ? My grey cells seem to have deleted it. :roll:

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Re: Launch Detection (almost)

Postby OverTheTop » Wed Dec 30, 2015 8:23 am

wavelength = velocity [m/s] / frequency [Hz]

= 300000000 / 433000000
= 0.693 m

Now I guess you want about a 1/4 wave
=0.693 [m]/ 4
= 173 mm

So that is the length for a 1/4 wave antenna at 433MHz. Having said that, it is likely to be close but not the exact length required. 1/4 wave antennas normally assume a flat groundplane at one end. This means the length calculated previously is a little too long, as we are not using a groundplane. The difference is very small and without some fancy testing and stuffing around it is probably not worth the effort to determine. I would go with that length if it were me.
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Re: Launch Detection (almost)

Postby lorstin » Wed Dec 30, 2015 8:50 am

Thanks OTT, much appreciated.
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Re: Launch Detection (almost)

Postby lorstin » Sat Jan 02, 2016 8:45 am

Has anybody seen my memory? I'm sure I had it awhile ago.
Did I say 433Mhz? :oops: I should have said 315Mhz. One more question for you OTT - does the first part of the formula remain the same ( 300000000 ) ?

like so.....
= 300000000 / 315000000
= 0.952 m
=0.952 [m]/ 4
= 238 mm
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Re: Launch Detection (almost)

Postby OverTheTop » Sat Jan 02, 2016 10:19 am

Yep. Speed of light (reasonable approximation).

299792458 m/s in a vacuum, and about 0.03% slower in air:
https://en.wikipedia.org/wiki/Speed_of_light
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Re: Launch Detection (almost)

Postby CATO » Sat Jan 02, 2016 10:39 am

That is cool, thanks for sharing OTT....

I love this forum....

"For example, for visible light the refractive index of glass is typically around 1.5, meaning that light in glass travels at c / 1.5 ≈ 200000 km/s" :shock:
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Re: Launch Detection (almost)

Postby lorstin » Sat Jan 02, 2016 12:57 pm

Thanks OTT, cut to length, soldered in and now working.
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Re: Launch Detection (almost)

Postby ROCKet STAR » Sun Jan 03, 2016 4:22 pm

lorstin wrote:I know what you mean about the lack of instructions when buying Chinese modules from ebay, however I see this as a blessing in disguise - saves alot of confusion.
Anyway I bit the bullet and bought one, complete with retro styling! At $4.39 for tx and rx I don't think you can go wrong.



I have played with these units a bit. They work well, however the advertised range and actual range, I have found, are really very different. The ones I purchased were advertised as having 100m range in reality they didn't have a reliable range of much more than about 30m.

One other thing worth noting is how to encode these things. You'll notice out of the box that one row of pins on the large IC that is in both the transmitter an reciever will be unsoldered, with pads that by soldering allow you to pull each pin either high, low or leave floating. Doesn't matter what you choose to do with each pin, as long as you do the same to both the transmitter and reciever. This will encode the setup, and make it less likely to suffer from interference from any other nearby unit.
Chris Barnes

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UKRA - L3

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Re: Launch Detection (almost)

Postby lorstin » Sun Jan 03, 2016 4:44 pm

Thanks for the info ROCKet STAR ( was going to write RS, but it didn't seem right somehow ), range shouldn't be too much of an issue for what I have in mind. I'll check out those pads though, sounds interesting.
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