$17 wireless Prop-To-Prop link (Don't do it!)

Rayman

I got this thing because it was the cheapest RF link I could find:
http://www.sparkfun.com/commerce/product_info.php?products_id=7815

Unfortunately, it has 2 problems working with the Prop, that took me more time than I care to say to figure out:

1.· The receiver only works at 5 VDC, despite what their "Walkthrough" might indicate.
2.· The receiver data output is very weak.· I guess I should have known what it mentioned testing at 10uA in the datasheet.

I wound up having to put a 1 Meg resistor between data out and the Prop in on the receiver side...

Anyway, here's the circuits in case anybody else wants to try it:

It's very easy to use:· Just use "FullDuplexSerial.SPIN" on both sides.· And, I set mode bit 3 on the transmitter side.

(I may try again to use 3.3 V on both sides, now that I have it actually working... But, the board even has "+5V" written on the power pins.)

I also put this info here:
http://www.rayslogic.com/propeller/Programming/RaysStuff/RaysStuff.htm

Note:· Sparkfun also has a nifty looking 2.4 GHz link for a few buck more, but is probably a bit more difficult to interface with...

Post Edited (Rayman) : 12/14/2007 2:43:54 PM GMT

mikediv

Rayman thats pretty awesome but can I ask what type of stuff would you use this circuit for?? I.E keyboard or other I am new and want to try and build all the stuff you guys post but for us newbies a brief why would be awesome thanks

kittmaster

I use this for a wireless project I have for a retro portable radio. Their is also an 8 bit encoder and decoder that can be had for 8 individual discrete channels for transmition and can be set to 2400 or 4800 bps

The overall range is around 2500 feet, pretty impressive for what it is.

Rayman

mikediv said...
what type of stuff would you use this circuit for??

I intend to transmit weather data (and possibly rss feeds, web cam photos, email, etc.) from a PC to a Prop connected to a display...·

Actually, I'm going to use a digital photo frame as the display.· The prop will construct a series of slideshow photos from data sent from the PC and the digital photo frame will be in slideshow mode and cycle through them...

Perry

These radios look very much like a product offer by robotshop.ca for only $6.99

www.robotshop.ca/home/products/robot-parts/communication-control/data-telemetry/on-shine-high-sensitivity-tx-rx.html


They also sell sparkfun products

Perry

Rayman

Interesting... There are some slight differences, but very, very similar. Only thing I don't like about this one is the relatively high current draw of the receiver. On the other hand, it has a disable input.

mikediv

Rayman thank you it sounds pretty awesome if you feel like sharingt I wouldl love to try and buil;d the same thing sounds like something I can use, can I ask what are you going to use for a display on the prop I bought the hydra system not knowing any better and it already has a display but I would like to use an LCD or somehting very small is it very complicated to transmit video?

Rayman

This thing has a miserably low bit rate, so I'm not going to be transmitting video... Rather, I'm just going to send very short weather type data, like "T=38F", for example... The Prop will construct the output video.

Fred Hawkins

Interesting link. They have cheaper ($4.99) yet: http://www.robotshop.ca/home/products/robot-parts/communication-control/data-telemetry/on-shine-low-cost-tx-rx.html

OT: but cool http://www.robotshop.ca/home/products/robot-toys/wild-planet-spy-video-car.html

Post Edited (Fred Hawkins) : 12/11/2007 9:33:23 PM GMT

bambino

Would the robotshop version behave the same as the sparkfun mod I wonder. At 5 bucks a pair I could do some owesome home automation projects without x10.

And the spy car is totally cool. imagine putting Beau's Overlay on that joker to feed back sensor data on that car! Anybody need there yards raked for some spare change?

Rayman

Sometimes I wish I weren't so cheap...·

The receiver was working fine when right beside the transmitter, sharing ground.· Just put the receiver on battery power and a few feet away and...· well, it's not so fine...· Lots of corruption in the data...

It's hard to see exactly what's wrong because the receiver output is so weak that even my scope probe seem to affect it...

I think I'll have to put in a mosfet to the receiver output.· I guess it's expecting 5 V cmos...· Or, maybe a 5 V logic buffer would be easier...

I'm starting to wish I bought something that works better at 3.3V...

Leon

The new TI eZ430-RF2500 kits are only $49, and work very well. I bought two kits when they were on special offer at half-price. They come with one USB interface and a battery-powered node. They have their own MCU which makes interfacing very easy.

Leon

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Amateur radio callsign: G1HSM
Suzuki SV1000S motorcycle

Post Edited (Leon) : 12/12/2007 2:15:48 PM GMT

Rayman

Leon: That does look pretty cool! Very powerful. But, it looks like a lot of work... Plus, it must be very popular, because everybody is sold out!

nice think about this sparkfun thing (if I get it working) is that it is extremely simple...

VIRAND

It seems to me to use the propeller to transmit on a CB, ISM, or unused broadcast frequency,
then use a regular radio as the receiver. For example, encode your data as morse code
and it should be easy to decode. The range should be within your home with so little power
and this method might cost nothing.

Rayman

I wonder what's at 80 MHz...

Paul Baker

80MHz is part of channel 5 broadcast television (in the US).

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Paul Baker
Propeller Applications Engineer

Parallax, Inc.

Rayman

Ok, I give up with these boards... I got one to work at a range of up to about 1 foot reliably, but it just goes crazy beyond that...

Perhaps it just the particular version that I have or something, I don't know...

I'm going to look for something else that works at 3.3 v.

I want to delete my first post on this thread. But, I guess that kills the whole thread, right? Maybe it's better that way...

Nick Mueller

> Ok, I give up with these boards... I got one to work at a range of up to about 1 foot reliably, but it just goes crazy beyond that...

Did you forget the antenna?

That thing *should* work. Your 1Meg-R looks *very* strange. If you look at the Propeller's datasheet, it says that the input-leakage is +/-1µA, a magnitude less than the 10µA output-capability of the receiver. You should completely leave out the resistor, because the receiver's output is sooo weak. If you are anxious, put some 100 ohms in between.


Nick

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Never use force, just go for a bigger hammer!

The DIY Digital-Readout for mills, lathes etc.:
YADRO

Fred Hawkins

Rayman said...
Ok, I give up with these boards... I got one to work at a range of up to about 1 foot reliably, but it just goes crazy beyond that...

Perhaps it just the particular version that I have or something, I don't know...

I'm going to look for something else that works at 3.3 v.

I want to delete my first post on this thread. But, I guess that kills the whole thread, right? Maybe it's better that way...

Rayman, were you using·the·wire antenna that they recommend?

Rayman

I was using antennas (just a piece of wire)... May not have been exactly the right length, but I don't think it's critical...
The walkthrough talks about it working without any antenna at short ranges.

I'm looking at their Bluetooth modules now. Since I want to transmit from a PC, this makes a lot of sense. It costs a lot more ($60 or so for the 100m range unit), but I want something that works (and works at 3.3 V).

sylvie369

XBee Pro 2.4GHz modules are $32 apiece. You also need a $6 board from Martin Hebel and about $5 worth of parts, and some time soldering it all together, but you get a MUCH longer range, and a lot more features·than a simple transmitter/receiver. At about $43 per transceiver, I think they're a far better deal than the other RF links I've seen. If you want to bring the price down from there, you can go with a regular XBee (not the Pro) for $19, bringing the total cost to about $30/unit, at the cost of some range (still should be a good range, though).

The XBee is a 3.3V device.

hippy

I've had similar modules work with 'random lengths' of antenna. It could be the lack of voltage for the receiver. You could try temporarily putting a 1V5 AA battery between the Propeller 3V3 and +V of the receiver ( 4V8 ) which might improve things. The amount of power from the transmitter is almost certainly proportionate to its supply so bumping that up should also help with range.

I like XBee's. Once configured ( a one-off operation in many cases, and that can be done by PC rather than using a propeller ) it's a simple case of send serial out, get serial back. Much greater complexity available than that if you want it.

Phil Pilgrim (PhiPi)

One thing I've learned the hard way with inexpensive RF units like this is that the antenna matters. At the very least, you should calculate a 1/4-wave whip length and use that. Unfortunately, that's not all. Simple vertical whip antennas need a "counterpoise", which could either be a 1/4-wave piece of wire connected to Vss and pointing down, or a ground plane, which can be considered a "virtual counterpoise". You can read about all that stuff here.

I built a radio-activated duck decoy once (which is now illegal to use) for a friend of mine, using one of the Micrel "QuikRadio" chips as the receiver. I couldn't figure out — even with a proper whip antenna on the duck — why the range was so short. As soon as I sat the duck on the ground, though, the range increased by an order of magnitude. The "real ground" was acting as a counterpoise, even though it wasn't physically connected. Since the duck was used on water, that worked equally well.

-Phil

Rayman

I think these things are what's typically used for things like garage door openers, keyless entry, etc... It should have worked at close range without an antenna. The datasheet said exactly what length wire to use as antenna, and I eyeballed that... I think these things are just defective... Perhaps a different batch would work better.

I think for Prop-2-Prop communications, the ZigBee, XBee stuff is definitely the way to go.

But, I want to go from computer to Prop, so I think the bluetooth module is better... (At least I hope so, I just ordered one from Sparkfun).

Phil Pilgrim (PhiPi)

Garage door opener and key fob transmitters typically use a resonant loop antenna, which can be etched directly into the circuit board. In any event, you certainly can't go wrong with the XBee modules. They just seem to work right out of the box and can be used with more of a "Tinker Toy" approach, since they come with proper antennas. Such an approach is simply not possible with the cheaper RF modules.

-Phil

computer guy

For the $17 pair spark fun has this in the description - "The receiver is operated at 5V and the transmitter operates from 2-12V. The higher the Voltage, the greater the range."

Just thought this might be worth pointing out.

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Check out my robot using the propeller RECONAUTOR

Rayman

read the "walkthrough.pdf" and you'll see it says that the 4800 baud units should work at 3.3 volts...

hippy

It's all very confusing on that Sparkfun page as none of the stock numbers tie up anywhere. The KLP_Walkthrough doesn't tie in with the page description nor with the Receiver datasheet. The diagrams in the KLP_Walkthrough don't match the picture on the page nor in the datasheet. The datasheet picture does look the same as that in the datasheet.

I suspect the KL_Walkthrough relates to an entirely different product and is provided for the details of software interfacing rather than as an electrical spec of the product sold.