Infrared HPWM setup

[richard]

if you look at the data sheet for a tsop4838 you will see that you have a numbers of issues to contend with


1. @9600baud the bit time is 100uS or approx 4 cycles of 38khz , about 2 to three times faster than the tsop4838 can cope with
2. the max burst rate is 800/sec a 9600baud stream can exceed that
3. after a 70 cycle transmission a 12 cycle min tx gap must be made [some devices can lock up if u don't and need a pwr cycle to recover]
4. the device will do its very best to reject a continuous transmission and go mute till a min tx gap in tx is observed, which is what you are doing.

overall tsop4838 is not particularly suitable for serial tx from a uart, you could try a much lower baud rate and you will need to
invert the transmission logic so that there no transmission at idle

i would also wire tx to rx directly to verify code works before trying ir link, also have a look at Manchester encoding and check out ir tx protocols like RC5/6 NEC etc

[astanapane]

Hi Richard,

you are right, i have decreased the speed and manage to play a lit bit with the delay in useconds.

I worked somehow but not always reliable.

I think i will try the RC5 method.

[richard]

I worked somehow but not always reliable.

the series resistor for the led is wat too big, it will make range / reliability pretty low. it could go as low as 39 ohms safely [probably lower even] in a non continuously on configuration otherwise 100 ohm would be better

[astanapane]

I will try to change that as well before i go for the RC5.

The following 15 days i will be in a business trip in Abu Dhabi so i will get back as soon as i have time to check this out.

Many thanks.

[tumbleweed]

You can get rid of the transistor and associated resistors and just connect the OUT directly to RB7.

If you need to, you can invert the RX sign with the DTRXP bit in the baudcon register.

[mpgmike]

the series resistor for the led is wat too big, it will make range / reliability pretty low. it could go as low as 39 ohms safely [probably lower even] in a non continuously on configuration otherwise 100 ohm would be better

For most LEDs or SSRs, I found 470 ohms offers a good compromise between response time and effectiveness.