Hi, I wonder if anyone has experience of hacking one of the cheap 433 Mhz keyfobs that can be bought on ebay ( **broken link removed**) in particular by adding an external antenna.
I have built a simple but reasonably effective portable data loging system which uses several these key fobs to transmit a simple state change (on/off) from up to four local sensors to a receiver. I chose these because they are very easy to get hold of, are very cheap and can be self contained using the internal 12V battery with a good battery life for field use.
I (carefully) remove the push button switches and then solder fine wires to the solder pads to give me four sensor inputs.
Having got my system working reasonably reliably well up to 50/80 metres I would like to extend their transmit reliability and range but cannot figure out where to attach an antenna to the key fob cct board, at 66 my eyesight is simply not up to trying to trace out such a tiny board.
I have attached three photos of a typical board (they all differ slightly but basic layout is similar) the first with the top of the fob removed and showing the metal rim around the fob. This is not connected to the board but I wondered if there might be some form of capacitive coupling making this an antenna??
Then there are photos showing front and rear. I noticed the track with holes bored in it looks like it might be an antenna but also what looked like a printed inductor on the front side.
Any pointers or help would be very much appreciated.
Purclewan.
PS the receiver has already had a 17.3 cm antenna upgrade which helped.
I have built a simple but reasonably effective portable data loging system which uses several these key fobs to transmit a simple state change (on/off) from up to four local sensors to a receiver. I chose these because they are very easy to get hold of, are very cheap and can be self contained using the internal 12V battery with a good battery life for field use.
I (carefully) remove the push button switches and then solder fine wires to the solder pads to give me four sensor inputs.
Having got my system working reasonably reliably well up to 50/80 metres I would like to extend their transmit reliability and range but cannot figure out where to attach an antenna to the key fob cct board, at 66 my eyesight is simply not up to trying to trace out such a tiny board.
I have attached three photos of a typical board (they all differ slightly but basic layout is similar) the first with the top of the fob removed and showing the metal rim around the fob. This is not connected to the board but I wondered if there might be some form of capacitive coupling making this an antenna??
Then there are photos showing front and rear. I noticed the track with holes bored in it looks like it might be an antenna but also what looked like a printed inductor on the front side.
Any pointers or help would be very much appreciated.
Purclewan.
PS the receiver has already had a 17.3 cm antenna upgrade which helped.