IAN LANG ELECTRONICS
So, in the last two chapters we messed about with a low cost TX/RX pair from Maplin. Let's delve a bit deeper into it and see if there's any easier short cuts we can find.
The hardware is made by RF solutions of
Lewes in Sussex, and as such I'll be quoting heavily and borrowing pictures from their datasheet about it quite heavily.
On the left is the receiver. It's a small device, known as the RR3 and measures
38 mm or 1 1/2 inches across the long face. It's 12mm (1/2 inch) tall, and 2mm (less than 1/12 of an inch) deep. Where the three pins at the far end are, the leftmost is pin 1. Then pin 2, pin 3, 7, 10,11,12,13,14,15.
You connect it according to the following manner:
And if you're doing it on a breadboard;
This particular circuit is one we'll be using later to do a small project. For now ignore the LM386 and speaker, we'll get to those shortly. The transmitter is even smaller and comes in two flavours:
On the top is the RT4, which is the type I've got, and the bottom is the RT5. Buying as a pair from Maplin, there's no saying which you'll get. It doesn't actually matter. Apart from the obvious physical build differences, The RT5 lacks a final capacitor section at the output. Meh. Here's the pin stuff:
And again if you're breadboarding:
I've shown a proper antenna here, it needs to be 15 to 17 cm but you can get away with two bits of wire. A proper one will increase performance slightly. Under ideal conditions the transmitter can do 70 metres (275 feet) but ideal conditions mean a 14V supply. They'll work as low down as 2V. I'm giving them 5V and a range of 25 feet or so seems reasonable.
They are amplitude modulated. If you dont know what this means, see the section linked to the left. Put simply, they are susceptible to interference. Keep them away from anywhere where a source of electro-magnetic interference is likely. They're basically a hybrid IC, which means as well as the normal chip construction there's a thick film printed on the surface. This means that there's an incredibly stable frequency and no fiddling about with little components to tune the thing.
The Baud rate from your Arduino has to be kept fairly low. You can't use these things at much over 4800 because it can't handle it. All it does is grab from the serial output and then transmit; at the other end it receives and puts out the serial input. There's a limit to how fast it can do this, so keep 4800 as the top.
I've gone back to front on this topic really, as one of the first things students do when messing with radio is to make a wireless doorbell or buzzer. Let's now remedy that flaw. Here's a short video:
We're going to use a slight variation on what's gone before as far as the output is concerned; it's designed to minimise the effects of intererence. So, over the page then, and let's have a look at how it does it.