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8 channel IR remote control (RC car featured)

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LAN_403

uzzors2k

Thu Dec 27 2007, 08:33PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

To do something different I thought I would try making a remote control system. It's based on two PIC16F88's, but with some software changes the PIC16F628 could be used instead.

The transmitter software will sweep through the inputs and set an array with bits according to how the input is. This is then sent via IR. The IR protocol I made uses a 2ms start pulse, followed by either 1ms pulse for logic 1 or 0.5ms for logic 0. There is 0.5ms between each pulse. The receiver reads this and puts it into an array. This array is then used to set the output pins. Basically it uses parallel data acquisition, so multiple buttons can be pushed without errors. I've made it so it will only send a new IR pulse train if the inputs have changed as this saves power. The only disadvantage I have found so far is once the receiver looses reception it will continue with what is was doing. No good for RC planes or helicopters!

Of course I had to test the setup, so I found an old RC car with no remote and rebuilt the electronics from scratch. Range is poor with the current IR system, only 1 meter

but it proves that the concept works. Bending over the car and running with it everywhere isn't too practical though, so in the future I'll switch to an RF system. All you hams out there - is it feasible to make an RF transmitter/receiver pair with ~50 meters of range? I haven't put much thought into frequency, but either 25 -30MHz or FM frequencies.

Here are the source, firmware and schematics.

]1198787565_95_FT0_8ch_ir_remote.zip[/file]

Bjørn

Thu Dec 27 2007, 09:27PM

Registered Member #27 Joined: Fri Feb 03 2006, 02:20AM
Location: Hyperborea
Posts: 2058

You will be able to get alot better range with fewer parts using IR, just keep on hacking. Usually fewer parts means more complex software, that means you learn more.

A PIC can send radio signals using 100% software, both FM an AM. I made a software transmitter I could recieve on a normal 96 MHz FM radio. To generate FM you need to mess with the oscillator/crystal to make it generate different frequencies. AM is much simpler, in the simplest case you just connect your 38kHz (higher is better, I used 12 MHz) to an antenna or just a short wire and modulate it. And you receive the harmonics at some multiple of your frequency unless you have a reciever that can reach it directly.

I have made both my PC and a PIC transmit more than 50 metres without any external parts.

HDR

Fri Dec 28 2007, 01:20AM

Registered Member #1165 Joined: Sun Dec 09 2007, 04:41AM
Location: GA, USA
Posts: 35

Could you post an example/explination of how to get a PIC to do this? I'd like to build a cheap radio for 2 meters, since a power spike in my moms car fried my HT a few years ago... And a weak software radio and a power amp seems like it'd be a lot easier to build than a regular radio.

LarsE

Fri Dec 28 2007, 01:53AM

Registered Member #153 Joined: Sun Feb 12 2006, 03:44PM
Location: Sweden
Posts: 31

I would have used a logic-level FET to drive the IR-led and do all the modulation in the software, you can also decrease the duty-cycle so you can increase the led current and get better range.
Also using a header pulse and a parity bit can be a good idea for increased error detection.

uzzors2k

Fri Dec 28 2007, 12:25PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

That's awesome BjÃ¸rn, I had no idea it was so easy to send RF. The hard part will be making a receiver...

I simplified the circuit so modulation is done via software, this cut the amount of external transistors down to 1. I also reduced the IR LED resistor size, and added a capacitor for larger peak currents. The range has doubled which is good, but it's still less than a standard TV remote can boast. I think the carrier frequency might be off, causing the BPF in the IR module to limit the range. I'll see if I can get it closer. Here are updated schematics and firmware.
]1198844721_95_FT36533_8ch_ir_control2.zip[/file]

Tom540

Fri Dec 28 2007, 03:51PM

Banned on 3/17/2009.
Registered Member #487 Joined: Sun Jul 09 2006, 01:22AM
Location:
Posts: 617

Are you using a matched Tx and RX diodes? Or you might try using three IR LEDs in paralell. I recently bought one of those really tiny IR controlled helicopters and the range on them is amazing. I had it 3 stories over my head and could still control it.

As far as radio I have a schematic for a 303Mhz AM Rx and TX Ive used on a robot project. It's pretty simple. Ive attached the receiver if you plan on using it ill dig up the TX for you. Digikey stocks all the parts. I just noticed the op amp is actually a opa2347.
]1198857083_487_FT36533_303mhzrx.pdf[/file]

uzzors2k

Tue Jan 01 2008, 01:09PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

If you could find the transmitter that would be great Tom. The receiver looks nice and simple. Most I've seen have multiple transformers, inductors and capacitors that all need tuning.

My scope was uncalibrated giving 10% error, so when I tuned the transmitter for 38kHz it was actually at 34kHz. I set the carrier to 38kHz and the range has doubled again. I think it's about as good as it's going to get now. The receiver has a small reception cone which is fine for TVs and stationary objects, but no good for a moving car. Since the receiver is mounted on the roof it almost never gets a clear line of sight and must rely on reflection. I'll spend time working on RF instead.

Corrected firmware. ]transmitter.zip[/file]

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