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IR-GhettoBlaster.php   11738 Bytes    02-02-2015 22:02:53

USB - IR - Transceiver (aka Ghetto Blaster)

This nice gadget directly uses the bitstream coming out of the USB-UART-Adapter to key an oscillator (on/off), build around a NE555. The carrier is approx. 38 kHz, close to those of a Remote Control. Just louder :-)   A recycled IR - Receiver provides an rx path.

Micro-Projects • Tools : USB - IR - Transceiver (aka Ghetto Blaster)

USB - IR - Transceiver USB - IR - Transceiver

Circuit Description

The circuit uses the USB-UART-Adapter as an interface to extract the UART data. With the TX signal a NE555 is on/off keyed by means of the RESET pin. The so generated 38 kHz bursts are amplified by a FAN3225 which drives the SPP80N08S2L-07 (Logic Level Power-Transistor) which switches the LED matrix. The used LED's are OFL-51 which operate at 940 nm and have an aperture angle of approx. 10°, as it is intended for an unvisible point to point datalink.

An inverter has been inserted in order not to have the IR-LEDS always on when the bus is idle. The resistor for the carrier oscillator (R2, now 16kΩ) had to be optimised empirically, as calculation yielded a frequency slightly below. For the RX path, we used a TSOP39138 (IR Receiver Modules for Remote Control Systems). It was selected to match the carrier frequency from the NE555 as well as the wavelength of the diodes. A lot of different types are available to match nasty environmental conditions.

Configuration (USB-UART-Adapter)

The device must be configured before use. Microchip offers several tools to do so. You may freely choose a VID (vendor ID) and PID (product ID) as long as your project will not escape your lab. (In case you leave the door open : a wrong driver may be loaded :-) So be careful ! You may lock yourself out when using a different VID (default:0x04D8)

We suggest you use the following settings : (Tools are from Microchip Website)

Configuration of the MCP2200

(Self) Test

The device now sends to the (white) ceiling. We record the received (reflected) data with a terminalprogramm - and with an oscilloscope. The picture says (not all) but a lot.

Hello World

Now as we have that much (transmit) power, it may be interesting how far can we reliably transmit and receive data. To measure that, we must develop a website on BER (Bit Error Rate) first. This test will be added on a later time.


USB - IR - Transceiver USB - IR - Transceiver

USB - IR - Transceiver USB - IR - Transceiver

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t1 = 3943 d

t2 = 551 ms

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