Keyless Entry (Tx Rx system)

[daviddoria]

I am trying to make a keyless entry receiver/transmitter for a car.

I know that i need a 2 transistor oscillator to create the carrier wave... all the tutorials i've seen are so you can send like digital logic style stuff on the wave... if i just want to have a "lock" and "unlock" signal then this shouldn't be that hard....

pretty much all it has to do is complete a circuit inside the door....
so i need like 2 switches that only serve 1 function each...

should i use an AM or FM transmitter? do i just need the carrier wave since it is such a simple on/off type thing? or do i need to ride something on it?

i guess the hard part is inside the car door... i actually bought one of those kits that comes with the receiver and the transmitter... but i couldn't get it to work... there were like 8 wires on each switch in the door... anyone know about car door locks? i would imagine there are just 2 wires that you short to trigger the lock solenoid...?

 

[Skyknight]

I'm very interested in that project too.
Of course, if you're gonna use legal frecuency bandwidth, you shoudn't prepare the receiver only for a simple signal or any accident could open your car. I encourage you to send a code. This way, only you would be able to open your car. What do you think about it :?:

 

[Gene]

Don't discount the digital encode too quickly. You don't want your car doors to lock/unlock everytime you drive past a radio station tower

 

[daviddoria]

really for right now i don't care... i just want to make this turn on an led across a desk or something... just to get this basic idea of how to get an on/off radio signal (to be used in remote control car applications)

i can then later worry about the car door application.

Transmitter:
i've been looking at something like this for the transmitter:
https://www.aaroncake.net/circuits/fmtrans.htm
that has a mic for the input, i would just have a switch (would it have to go through a capacitor) for the input (like "ON")

Receiver:
all the receivers i've found have been exceedingly complicated. Probably because they are designed to decoded the message that has been sent lol. I just want it to say "ahh yes there is a signal, turn on the LED"

hehe i hope you understand my goal

if anyone can roughly explain the function of the 2 transistors in the transmitter schematic that'd be great.. maybe thats a good starting point.

david

 

[bogdanfirst]

i think that transmitter is not suitable for your application. the thing is that it is on the frquency range of a normal radio FM band, so you might get triggered by music on the radio....i htink that you dont want that.
and i might suggest one idea! you can use a receiver and emitter from a remote control car. the transmitter is quite small(there are remote controlled cars that have just one button or 2) so you can use them. the receiver is usually small too.
or you can use a simple radio oscilator on a lower frequency and simple receiver, like one with 2-3 transistors. one push-open, push-closed and so on. .....
if yo want to use that transmitter you can generate an audio frequency and send it to the transmitter. as a receiver you can use a simple radio, a pocket one, wich i think that it is small enough. then use a tone detector at the output of the radio so you can only get triggered by the specific signal.
have you thought IR ? not such a good solution.....
what about ultrasounds, it is a good idea, maybe get the car opened by whiseling?

 

[daviddoria]

again, the aim has been shifted to simply get an "on/off" type action across the room.

also, i built the transmitter that i posted a link to earlier. it is very hard to tune to my tranmitter on the radio... how would i increase the "lock" on the radio? i used 2x 3.3pF caps in parallel instead of the 5.6pF.... does that matter?

david

 

[bogdanfirst]

2*3.3=6.6, wich is one pF more than 5.6, so it might be a problem with it.
also, for these small values, they can vary very much due to the fact that the leads can increase capacity.
but do you mean that you cannot find it on the radio, or that the frequency is not stable? you have to tune it all the time to get a good reception?

 

[daviddoria]

yea.. i have to really fight for it to come through (i've tried several frequencies as far away from big radio stations as i can). I can't get it to "lock in" as was the case when i bought a transmitter kit and put that together, i could turn the variable cap and then all of a sudden the static would just stop completely and it would be perfectly clear.

also... still looking for help on a "on/off" type radio receiver...

 

[bogdanfirst]

if you have a radio with a TUNNING led, then you can hook op a Flip-Flop to it so that when you emit with the transmitter, the led will light and will turn what you need on/off
you can try to build a simple 1 transistor emitter and 1 transistor receiver tapped on the same frequency. emit and you get a signal on the other end. or you want to have 2 signals, one for ON and one for OFF?

 

[daviddoria]

yea, now we're getting close... a 1 transistor emmiter and 1 transistor receiver sounds fantastic... do you have a link to a schematic or can you explain how to do that?

thanks alot

 

[Gene]

David - I think that choosing a matched pair (transmitter/receiver) would be a good idea. They would be designed to work in the same frequency. I searched last night but was unsuccessful. I know somewhere I have a simple schematic for this. I'll look again when I get some time.

 

[daviddoria]

excellent, thanks gene, and yes, that's exactly what i'm looking for, simple, single (mabye 2 if its not that hard) frequency tx/rx set.

i was unsuccessful in searching as well, thats why i asked here

 

[lavenatti]

**broken link removed**

Check out the "simplest RF circuit" and "simplest RF transmitter".

If these work for you I think they are just what your're looking for.

Lou