Idea for Cheap Wireless Serial

RubrChicken

I saw some cheap brandless RC cars at my local generic junk store. I thought "Why not?" and bought two for ~$5 each. After driving them around the floor for 30 seconds (as long as the battery would last) I ripped them apart. They seem to be a three channels emulating two. There are some magnet coils in the front of the car that pull the wheels back and forth, and a motor in the back that can go both ways. I decided not to mess with the steering and just ripped the wires off (they were enameled and about 500 AWG). The actual circuitry is teeny tiny surface mount ICs, so I decided not to rip them off for fear of loosing the whole receiver setup. I figured there are three states for the motor:
Off- 00 (Ground,Ground)
Forward- 10 (1.5V,Ground)
Backward- 01 (Ground,1.5V)

I thought you could use this as an easy wireless serial tx & rx pair! Hook up the prop to the disassembled transmitter buttons, and read what happens on the other end. I'm not sure how fast this would go, nor if interference would be a problem. Feel free to comment! I have no idea if this will work-- just throwing it out there as a cheap way to get wireless up, as its only $10 for full-duplex (if it works).

I might attach pictures of taking apart the cars and transmitters, if everyone asks nicely.

Oldbitcollector (Jeff)

Did you buy cars on different frequencies? That might be a catch in making tx/rx work at the same time.

I love the idea! Post some pics, and if the source is a national supplier. (Radio Shack, walmart)
include that as well. [noparse]:)[/noparse]

OBC

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RubrChicken

They work on 49mhz, and are both on different parts of the band. If I have both receivers on but one transmitter on, they both respond. If I have everything on, the right receiver responds to the right transmitter.

I got the cars at Big5, they were on sale for half price. I'm sure you could find them all over.

virtuPIC

There is another thread on a Bell 202 modem - 1,200 bps on audio frequency - now at the object exchange. Haven't looked at the code so far but from the description it looks like a gemstone! If I remember correctly it even has some schematic for connecting it to a radio. You could also buy some cheap audio hand radio and use the Bell 202 code for transmission.

No matter which transmission you use: Do some error detection / correction!

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Tesla

Anyone think that DTMF in short burst over FRS(family radio system) could work? You could not use it for continuous use, but in burst asynchronously.

Mike Huselton

DTMF has always worked for me. Disregarding the slow baud rate - Ma Bell tested DTMF to destruction and it always worked, even through a nuclear magnetic pulse.
Nah - just kidding about the EMF pulse. But it is extremely noise-tolerant.

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JMH

mctrivia

i am planning to buy some 45km 1000 channel walkies talkies. about $100 but would give long range communication and could still use the walkies talkies for other things. The ones I am looking at have a voice activated mode so by starting a carier wave a little earlier then the signal they don't need to be rewired at all.

Bell 202 modem looks like the ideal way to go for this project.

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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.

RubrChicken

I was trying to make something about an order of magnitude less in cost... Pictures are coming.

mctrivia

yes my idea is not cheap but the walkies can still be used as walkies when not used with the project so really the cost is the 2.5mm jack to plug in on each side. Very cheap for temp projects like my turret which the only time I need the wireless link is when shooting 360x360 and don't want myself in the line of fire(should mention it is a camera on top of the turret).

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Need to make your prop design easier or secure? Get a PropMod has crystal, eeprom, and programing header in a 40 pin dip 0.7" pitch module with uSD reader, and RTC options.

RubrChicken

The pictures!

RubrChicken

Ken had something like that going with ham radios, and he said it could go two miles. With even the most basic license, you can legally transmit with over 1.5kw of power! Of course, that's providing all the electronics in the home don't melt first. (not the prop... >170C!)

Ken Peterson

If you're looking for a cheap wireless communication method, another option is to use the 315 MHz and 434 MHz transmitter / receiver modules at www.sparkfun.com. I think you can get a pair for $10 or so.

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hinv

hi mctrivia,

What radios were you planning on using? I know it is a little off topic since they are not in the "cheap" category, but 28Mile range is pretty good!

Thanks,
Doug