TECGRAF DOC

How to transmit data using a cheap RF module through USB. The circuit receives energy from the USB port (may provide 100mA and with some programming you can reach 500mA)

List of Materials:
1 - One pair of RF module (like Laipac RLP/TLP433A) look after it in sparkfun.com (they have different operating frequencies: 315, 433 and 917(?) MHz)
1 - TSUB3410 - Serial-to-USB integrated chip (QFP-32) from Texas Instruments.
1 - One Power LED (you may skip it)
1 - 3.3V LDO (Low Drop-out) regulator - to connect in the +5V (+/- 10%) line from the USB.

Start with the "walkthrough.pdf" guide, after it we will improve the wireless link to be connected to an USB port.

! ! ! - Altought it may look like a very simple circuit (just the RF link), you may find some rocks in your pathway.
I still don't know if this is a reliable circuit..so be carefull where you are going to use it. Be advised to try this circuit ONLY when you are in a good mood! if not go play PS2...otherwise this can damage your parasympathetic nervous system!

Step 1: Checking RF Modules

First of all you must go exactly through the steps written in the PDF file attached to this site ("walkthrough...")

It´s a good idea to check first the modules. Do it on a breadboard, it works? Fine, move to the next step... or check connections, wires, supply (did you turn it on?).

You can check the wireless link with an osciloscope or using any (hyper) terminal software. Check the maximum baud rate! (mine 4800bps). You may need a MAX232 chip, it is a Serial level converter...
[ PC >> MAX232 >> TX ] ~~~~~~~ air ~~~~~~~~ [ RX >> MAX232 >> PC ]

email me...may be I can help you!

Step 2: Improving the Circuit to Use USB Instead the Serial Port

If you are fortunate as I was, you can use a Rapid Protyping Machine like the LPKF C-Series. This way it allows you to use a little bit more complicated SMD (Surface Mounted Devices) IC.

Receiver:
Some times is quite annoying to change batteries, so we decided to supply the receiver from the USB port. It´s very simple, the USB delivers +5V (+/-10%), so the only thing you need to do is attach to it a voltage regulator (using Low-Dropout regulators is a good idea).

To interface the RF receiver with the USB we are using the TUSB3410 Serial-to-USB module. It´s a very simple chip and you may find it at, almost, every big supplier (?). We power it with 3.3V, regulated from the USB port. (Don´t forget to install the drivers that you may download from Texas Instruments web site)

When I connected the Receiver to the TUSB I had a problem. The Serial In port from the TUSB3410 has a strong pull-up resistor, so every data that I received was with a threshold of 3.3V (look at the internal schematics of SIN port in the datasheet...). So we plugged a buffer between the receiver and the TUSB4310.

Transmitter:
Straight foward! Just follow the basic schematic and it must works perfectlly.