I would like suggestions for a cheap, simple radio control device for the Propeller

ElectricAye

The scenario is this: you're driving your car and you want to activate a small battery-powered device that's attached to the top or rear of your trailer or RV, so the distance would be less than 100 feet. You push a button, perhaps something like a key fob, and it sends a short, simple signal to the device so the device will turn on. Communication only has to go from the driver to the device, so no acknowledgement of signal reception is needed. Timing is not critical, so I suppose the bit transfer rate could be fairly slow. Security is not a big deal, so it doesn't need any kind of fancy encryption or whatever. Most of all, the receiver needs to be small, cheap, lightweight, use as little battery power as possible. The only message that needs to be sent by the fob is probably something like a simple code, maybe similar to what's used on garage door openers.

Oh, and did I mention it has to be cheap? I'm hoping under a few dollars for the receiver, if that's possible - quantities could be ordered in the 20 to 50 range, I suppose.

Suggestions, especially from those who have experience actually using such a device, will be warmly received.

Thanks.

Dr_Acula

I have built these but prebuilt ones are so cheap now http://www.ebay.com.au/sch/rfremotech/m.html?hash=item3a796de5c9&item=251145348553&pt=Motors_Car_Truck_Parts_Accessories&rt=nc&_trksid=p4340.l2562

momentary or latched, eg 2 channel Rx and Tx for $15.

Lots of different products from that seller - multiple relays if you want them. I have used a number of their modules and they work very well.

Duane Degn

They aren't very cheap, but I like SparkFun's Nordic fobs. They use the nRF24L01+ transceiver. You can get nRF24L01+ transceiver modules off ebay for about $2.50 each. So your receiver end shouldn't cost much.

There's code to use these with Propellers and AVR chips. I think I have some modified code to send and receive with ATTiny84 chips(I'm can't remember if I got this working correctly or not) as well as code to use these with the Propeller. There's also code to use the Nordic modules with Basic Stamps (by Ron Czapala).

xanadu

If radio control rules out IR then it will be hard to find anything at that price. It would be cool if you could use the vehicles chassis as an 'antenna' between the remote and outside unit somehow.

The least expensive RF module I found was $3.95, where is Erco on this?

Phil Pilgrim (PhiPi)

ElectricAye,

If the "device" attached to the receiver is a large dot-matrix display that, when activated, says, "BACK OFF, IDIOT!", I would submit that your liability insurance alone will exceed more than a "few dollars" per unit.

-Phil

ElectricAye

Phil Pilgrim (PhiPi) wrote: »

...
If the "device" attached to the receiver is a large dot-matrix display that, when activated, says, "BACK OFF, IDIOT!", I would submit that your liability insurance alone will exceed more than a "few dollars" per unit....

LOL. I wish. Road rage being what it is these days, no doubt that's true. But this is a fairly boring application involving horse trailers, cameras, and some lady who thinks people are harassing her horses when they're on the highway. I suggested PIRs but she wants a button to push. And, you know, it's such a good idea of hers, she's thinking of having lots of them made and selling them. Who am I to say no?

ElectricAye

To Dr Acula, Duane, and Xanadu,

thanks for your inputs. All of your suggestions look good. I'll need to learn something about radio, I suppose, since I know diddly-squat about it. One of the things that always strikes me about making an actual consumer product is how much of a hassle getting things packaged is. For example, you can't just hand somebody a protoboard with a button on it and say, "Here ya go." No, instead it's gotta be packaged in some kinda fob thing with fancy buttons and all, and all of that stuff costs money. Unlike a lab, where I have wires dangling all over the place and duct tape galore. Am I wrong or is working with the general public just so tedious?

Sariel

Recently I have been looking for the same sort of thing. I considered the propeller, searching the forums for a way to maybe send a tone using the FM generator the Phil warned us against using because of FCC regulations. Using a tone broadcast across the airwaves, having another propeller scan for this and activate a relay. After doing some more thinking about it, and a few more web searches, I came to a conclusion. The prop is unfortunately not an ideal solution. If this is something for personal use, might I suggest the same route I am taking. Wireless door bell. If you don't mind a bit of hacking, there are a couple websites that show you how to do the modification with very little extra parts. (one transistor, the relay, and a few wires). here is an addy for you to browse:

http://www.hackersbench.com/Projects/ding-dong/main.html

The best part of this is, you can get one of these from your local hardware store for MUCH cheaper than you could buy the parts for and spend your time developing a propeller solution, even before calculating in the shipping costs to get bare prop parts from say, Digikey.

Invent-O-Doc

Although not as cheap as some of these other options, I keep lots of XBee modules around. They are small, easy to use, reliable and $19. There is a robust object for the propeller, but they can be used with any chip, sometimes even without a microcontroller at the transmitter end. (otherwise recommend the nordic fob, though i haven't used one)

ElectricAye

To Sariel,
yes, hacking a doorbell might be a good way to make a demo system. The guts of that seem to be similar to what Dr Acula pointed me to. Using a doorbell pushbutton on the dashboard might be a better idea anyway, so the lady isn't fiddling with her key fob while driving on the road.


To Doc,
Yes, I thought about using an Xbee. It seems like a logical choice, certainly for a prototype, but I'm hoping to keep the price down in case more than one unit needs to be made.

lfreeze

I built an attic fan controller using the radios on this ebay link.They are cheap and have
Worked without problem for a few years.

http://www.ebay.com/itm/1000m-4CH-Wireless-Radio-Transmitting-Module-TM1000-4-/300365598554?pt=Garage_Doors_Openers&hash=item45ef2f4f5a.

Larry

ElectricAye

lfreeze wrote: »

...They are cheap and have
Worked without problem for a few years...

Larry,
thanks for the recommendation. It looks like the same thing Dr Acula suggested, so I'm starting to see a pattern here. How exactly do you interface them with your Prop? Any particular code you use with these?

lfreeze

Here is the transmit test code. I can’t find the receive program. I will keep looking. It’s fairly simple,
A high on any or all of the four radio transmit data pins will produce a high on the corresponding pins
On the receive side. Use the attached diagram to make your connections.
_______________________________________________________________________________________
{{

CHINA RADIO TRANSMIT TEST 9 20 2009.SPIN

PROPELLER PIN 17 CONTROLS THE GROUND SIDE OF POWER TO XMITTER
VIA THE ULN TO GND PIN OF THE TRANSMITTER.

PROPELLER PIN 16 CONTROLS WHETHER PIN 10 ON THE TRANSMIT MODULE
WILL SEND A HIGH OR LOW TO THE RECEIVER

PIN 18 CONTROLS THE LED (BREADBOARD).

}}
CON
_clkmode = xtal1 + pll16x 'Set clock to 80MHz
_xinfreq = 5_000_000 'Crystal is 5MHz.

PUB LIGHTRECEIVELED

REPEAT
waitcnt (20_000_000 + cnt)
dira[16..18] ~~
REPEAT
OUTA[16..18] :=%111
waitcnt (10_000_000 + cnt)
OUTA[16..18] :=%000
waitcnt (80_000_000 + cnt)

ElectricAye

lfreeze wrote: »

Here is the transmit test code. I can’t find the receive program. I will keep looking. ...

Hey, thanks! Very interesting. Mind if I ask how long (or short) can the antenna be?

lfreeze

The modules come with a wire loop antenna. It measured about 17CM long. The working range I have been using is approx 50 feet. I never did a total distance test.