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High speed?

Clemens Valens's picture

How fast is your system? And does it need special high-speed infrared LEDs for it? I mean, all LEDs are pretty high speed.


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Sigo's picture

Submitted by Sigo on 29 August 2014 - 12:44am.

Hi Clemens,
yes, it have to be high speed IR-Diodes (TSHF5410 or TSHF5210 or similar) with rise times in the 25..100ns range or little more. Normal speed IR-LEDs with typical 0.5µs or so rise time is not enough, but works at lower distance range. (About 1/4 to 1/3 or less that far)

The TSOP works at a modulation frequency of 455kHz or 2.2µs for full periode, this tells why high speed IR-LEDs are needed.

Using high Speed LEDs, you can easilly transmit RS-232 over 15-25m !

I am using BASCOM with a little in line assember code for sending the 455kHz modulated signal. The rest is BASCOM.
One complete sent out scan takes as short as sending one Byte via RS-232 @ 19.2 or 34.4kBit/s.
This is about 1/19200*15 seconds = 78µs. (times 15 because of 10bit for sending the data und 5 idle bus time needed for recovery of the TSOP's AGC-Amplifier.

But the Basic program needs longer. I realized times of about 0,3 to 1ms for a complete cycle including user interface via RS-232 and so on, writing the result to the RS232 output at the same speed as the transmitter. If it is only up to pass an interrupt or event to another controller you can go faster to about 100 to 200µs.

BTW: I am simply sending out an RS-232 object, with 8N1 coding. Echoed singnals appear on the RS-232 Rx input, so that BASIC can receive the receive the result without stress.

And the RS-232 can still be used as user - interface.


Very fast long distance 90° or 180°-IR-"Bumper" for Robotics with direction detection

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