I am working on something that calls for a simple Tx\Rx that can control 4 relays independently. 30-40ft of range should be enough. I want to make it myself. I have seen ASK modules and such but haven't really studied them. The simpler and cheaper the circuit, the better. Waiting eagerly for your suggestions!

Simple but works. Two chinese r/c cars and mod the circuit within. Two aerials (of course on largely different frequencies). If direction is not an issue, one chinese t/x with some Transistors wired up to the receiver (for independent control of the relays) should do the job ??

I have tried that. Cheap chinese toy cars(which can go fwd/bckwd and lft/rght) can be used to control 4 relays independently but they need a huge capacitor on the output side or else the relays continuously turn on and off. Moreover they are quite unreliable(Lasted for about 3 days). The circuit I used had TX-2B RX-2B chips. And the range is dismal, 10ft at most.

http://www.hobbyking.com/hobbyking/store/__26864__433MHz_Superheterodyne_3400_RF_Transmitter_and_Receiver.html

A simple (and original PPM) design runs around creating an astable multivibrator and using timing capacitors to delay the pulses to form a PPM.
You could also use a mc like ATmega 8 to generate these pulses and feed them to the RF circuitry for transmission. On the receiver side, a 4017 counter can be used to decode these to various channels. Or again a programmed AVR to do the same.

http://www.sm0vpo.com/use/rc_enc_02.htm

For the TX2B-RX2B combo, have you tried using some high power drivers like 2N2222 to drive the relays, with reverse biased diodes to stop back e.m.f. Also, the TX2B provide unmodulated output at I guess pin 8, this can be fed to a decent RC circuit for increasing the range. Havent't tried but sounds it should work

you can use 4017 decoder and encoder to select upto 8 channels individuals.
But after decoder, you need another circuit (Just like servo, but not linear, rather like switch) which can sense the pulse width received in each channels if >1.5 mSec and latch for 1 complete cycle (20mSec) or till it is not set/reset.
But if you want easy switching channelling IC, here are those
http://www.rentron.com/Files/CIP-8.pdf
http://www.rentron.com/Files/CIP8_TWS8BIT.pdf
http://www.rentron.com/remote_control/R-8Px.pdf
http://www.rentron.com/remote_control/8P-ENC_DEC.PDF

http://www.glolab.com/encdec/gl/app.html

http://www.robokits.co.in/datasheets/HT12E.pdf
http://www.robokits.co.in/datasheets/HT12D.pdf

using laser LED (Not true laser but made linear using lens ) and Phototransistor, you can increase range. You can even use RF Link using single transistor FM Transmitter and single transistor super re-generative receiver with LPF used in toy car section. All you can get at CheapRadio/Naresh/GeneralRadioCo./Reltron/Vishnu/AjayElectronics at ChandniChawck, Kolkata. You may wait sometime after order for processing.

Just select IC as per availability.
You can make even DTMF Tone control for decoding and encoding using 8870 and 91214B IC.
http://www.electronic-circuits-diagrams.com/remotecontrolsimages/remotecontrolsckt5.shtml

All are proven. Just you need to order components, and Go.
You can consult with VKSingh as he started robotic shop.

Thanks

Options :

1. You may increase the range by amplyfying the Tx Power with RFAmplifier using ASK Modules. Just add 47PF to Tx antenna and amplify using an BF494 transistor with a tank at collector and an telescopic antenna.

2. Just Purchase FM Microphone (35/- hardly), FM receiver with Gang control (with TEA5591 IC not CXA1019) an DPDT switch, uM66 musical IC, Small Speaker, Tuner Knob and some resistance. Then just replace condencer mic with dpdt SWITCH, um66 ic AND ENCODER. Tune in receiver using DPDT switch and speaker/Decoder. during tuning, connect UM66 as TX in and speaker as Rx out. after tuning, just switch over to decoder and encoder, and you get an 100-120 mts remote control.

@kalyanprodhan, the um66s are still made? I can never forget the tu du du du du du du di da du of those...lol...great ideas there.

And I thought there was some plug and play ic for this I am doing instrumentation engineering and remotes are not a part of my curriculum yet, so a bit fuzzy on the theories explained. I will get into this after my sem. Thank you everybody

The purpose of this remote:
To control a dual h-bridge made of four relays. The h-bridge will be used to control two brushed dc motors. So I do not speed control.

@lastRites, if you do not need 'coasting'/'free running' in the hbridge configuration, here's a schematic using which you can have direction control and braking using only two relays and two control inputs. And there are no shoot throughs

When I was a kid, I made this circuit by pondering on how i could hook up two relays to switch direction on a dc motor, at that time I knew nothing about an H bridge or if such a configuration could ever exist (we used to have big plastic encased relays then) but I use it till date for little applications, the recent one was an auto water leveller .

Hope it helps whenever you start

BW
GS

I have had the h-bridge ready for ages I just need to trigger the relays remotely. I just do not want to crack up a 400 buck car just to get the remote So I am looking for some alternative. Besides I like doing little electronic projects..

If you want only H-Bridge, then just use Toy Car Remote (Full Functional) with Tx-2 and Rx-2 IC. In any car costs Rs. 250/- +, you will get this. Then just cut some foil and fed the power to your driving MOS (More technically V-MOS for power use). The existing circuit was driven with C8050 and C8550 Transistor in Class -C Mode (Switching Mode). So, just use existing driver 8050 and 8550 as a driver buffer stage and FED to Main Power MOS.

Please note,
1. MOS may need Heat Sink, you need to consider.
2. Switching surges for Mechanical Inertia and Motor Back EMF should be smoothed using Snubber RC circuit. Else, VMOs may damage.
3. The power feeding line should fed the Rx and power line through LC Filter so that switching surges may not disturb Rx Performance.
4. Tx Tank circuit (Here Crystal), Inductors and Rx Tuning Inductor and Capacitor may be shielded.

HT12 series ICs are available easily and can be channalised (Like plug and play) ASK Modules will be better for that. NO problem of NOISE in power line.

Tx2 and Rx2 ICs are much expensive rather complete circuit in cars. Reltron asks for Rs.890/ for a pair. In robokits, HT12 series ICs are less than Rs.80/- each.

Thanks

Hey trisit, What is the last progress ?

Thank you Kalayanda I used the toy cars' rc but still the same problems. Not reliable and glitches occur frequently. The other methods, I did not understand(I did not get time to read up on the topics). My exams are on now, so no real work will get done before the 14th. I would be much obliged if I can get some easy to follow steps to use the ASK modules as a 6 channel radio(I know nothing of encoding and decoding ). I am not asking to be spoon fed but for some links that would help me understand how to implement the ASK modules

You can use the standard 433 Mhz modules availables in the market(In kolkatat you can get them from Gemini,Chandini) or some other electronics store like nskelectronics.com or
http://robokits.co.in/shop/index.php?main_page=product_info&cPath=7&products_id=75
This are single channel,so hook it to a HT12D and HT12E to get a four channel easily 100-200 meters range in open , look into the data sheet to connect the rx/tx module to HT12D/HT12E ,they are easy to use .

As suggested, I went for the ask module and the HT12 series encoder decoder pair. They cost me Rs.275 and Rs.50 respectively. But I could not get either the 51ohm or the 1.1Mohm resistors.. I will post a detailed build log once I get it working.

Be aware, the resistances may trouble you to solder. Better scrap off by knife the lead and then insert in board and solder. I found this in common value resistance packets that gives trouble during solder.
You can add 33 Ohm and 18 Ohm in series or use 50 ohm. or use 47 and 3.9 ohm.
Also you can use 680K and 330K in series or 1M and 100K in series.
If the value be crucial, I prefer use 90% as fixed and 10% as variable resistance for high resistance only.

I too built a similar project last year. This guide was very helpful:

http://www.engineersgarage.com/electronic-circuits/dc-motor-control-circuit-wireless-rf

Feel free to contact in case you get stuck up somewhere!