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.
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.
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)
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.
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.
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