I still need an answer to my question. I need a way to test a repaired key FOB to see if it is transmitting. I don't care about codes or anything else. I would also like to know what frequency they work at. I am guessing in the range of 300-400 MHz.
The receiver has 4 pins labeled GND, VCC and two Data pins which look to be tied together. I would power up the receiver and place a scope across either data pin and ground. Place a key fob beside the receiver, push a button and see what you get. My understanding is N. American key fobs for automotive are 315 MHz. You should see the key fob data string. This is purely a guess on my part. You can also maybe take the data out and feed a opamp and drive a LED? I don't see any need for an Arduino. Looks like they use the transmitter and feed data in and then send the data to the Arduino.Hi Guys,
I bought a few of these 315/433MHz transmitter receivers and now I want to hook up the receiver portion to see if I can detect a signal from a Key FOB from my car or any other remote running on that frequency. Do I have to buy an Arduino to do this or is there a simple circuit using an LED that will allow me to see if the FOB is transmitting a signal? Thanks in advance for your help.
That's about what I read on them, high noise.I have one of those receivers. When you have a key nearby and press one of the buttons then you get a reasonably decent square wave output which contains the key data (usually Manchester coded). However with no key signal present they pick up a LOT of random background noise, so just checking for the absence/presence of data on the output pin isn't enough.
If you put an LED on the output then it will flicker dimly the whole time. When there's a key signal being received it will light more strongly. If you just want a basic visual check to see if the key is working then that's probably enough. But if you wanted to do anything more complicated then you'd need to hook it up to a microcontroller and decode the signal.
Are you placing the LED across both data terminals or to one and ground? I am just looking for a quick method with the LED but my plan is to hook it up to an Arduino in the long run.I have one of those receivers. When you have a key nearby and press one of the buttons then you get a reasonably decent square wave output which contains the key data (usually Manchester coded). However with no key signal present they pick up a LOT of random background noise, so just checking for the absence/presence of data on the output pin isn't enough.
If you put an LED on the output then it will flicker dimly the whole time. When there's a key signal being received it will light more strongly. If you just want a basic visual check to see if the key is working then that's probably enough. But if you wanted to do anything more complicated then you'd need to hook it up to a microcontroller and decode the signal.
The data terminals are one in the same if you look closely at the board so either terminal to common (GND). Like I mentioned earlier, also I have no idea how much current that circuit can source but bighand says it will drive the LED.Are you placing the LED across both data terminals or to one and ground? I am just looking for a quick method with the LED but my plan is to hook it up to an Arduino in the long run.
On a radio, you always have the carrier wave to tune into even when there is no voice/music signal to hear. In that case, you simply have silence. The problem with a key-fob system is that there is no broadcast when the button is not pressed so you have noise of any amplifed signal - especially if the board has an AGC amplifier seeking the weakest of signals (may be present, may be not). In any case, your best bet is to filter the output, not the input. I assume you have a 150 ohm resistor from the output to the LED. Put a 22 uF or 33 uF cap tied to ground and the other end between resistor and LED. This should cut off all flicker above 50 Hz to 32 Hz (respectively per 22 and 33 uF cap).Okay I hooked it up. 5VDC power and ground and the LED to data and ground. Power on and the LED comes on and flickers a bit (noise). I tried three different key FOBS and between the 315MHZ and 433MHz, I got all of them to flash through the LED. Any thoughts on removing the random flickering when a button is not activated? You can clearly distinguish between when it is random and when the key is pressed - solid flashing as opposed to random.
I have the LED placed across one of the DATA pins to ground with no resistor. The LED does not blow and it is bright when a key FOB signal is active and dimmer but flickers when there is not. I know the resistor is to drop the voltage for the LED and I did not measure the output signal voltage yet. Should I still use the same capacitor value that you mentioned in post #34?In any case, your best bet is to filter the output, not the input. I assume you have a 150 ohm resistor from the output to the LED. Put a 22 uF or 33 uF cap tied to ground and the other end between resistor and LED. This should cut off all flicker above 50 Hz to 32 Hz (respectively per 22 and 33 uF cap).
You need some resistance to make a filter. You can use a smaller resistor (half) but double the capacitance. My values were guesses of frequency. I didn't think you would be bothered (notice) by irregular flashes at 60hz and faster and I did to know what type if 'signal' you were getting from the FOB-induced LED excitation (flicker vs constant wave).I have the LED placed across one of the DATA pins to ground with no resistor. The LED does not blow and it is bright when a key FOB signal is active and dimmer but flickers when there is not. I know the resistor is to drop the voltage for the LED and I did not measure the output signal voltage yet. Should I still use the same capacitor value that you mentioned in post #34?