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[SOLVED] DE-5000 IR communication

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berger.h

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Helo ,
arrived at my DE5000 and I play.
LCR meter have unidirectional IR communication channel.
Depending on what I found out is actually the IR LED on the Tx of UART
I fint this project
The picture is actually a phototransistor L-53P3C connected to the USB to TTL UART CP2102
I use same phototransistor but different USB to TTL UART, I use PL2103HXD.

If I press PC button on DE-5000 and set on PC 9600, 8,1,None, receive on terminal only one hex 00 every 1s,
but DE-5000 send 17 byte stream every 1s.

Where there might be a problem?

USB.jpg
 

PL2303? The circuit is apparently depending on UART bridge internal pull-up, but it's not even specified for the Prolific chip. You might try with an external pull-up.

Generally check the RxD pin waveform with an oscilloscope.
 

You have true, PL2303HXD, it is my typing error. I measure voltage on Rx and is 3.3V without receiving, i.e. this input have pull up.
In the meantime, I did another test.
If I use old PL2303HX all working OK and in PC I receive 17byte
If use new pink **broken link removed** receive only one 00
If I connect TX and RX between old and new PL2303 and try send any data from one and then the other side all working OK.

If I measure the voltage on Rx (collector phototransistor) without receive
On PL2303HX is 4.2V
On PL2303HXD is 3.3V
Second difference, old version use external crystal, New version is without external crystal
 
Last edited:

I measure voltage on Rx and is 3.3V without receiving, i.e. this input have pull up.
Click to expand...
Proves only that it has some pull-up. The value may be unsuitable though. If it's high, the Rx rising edge is too slow to achieve a correct 9600 baud pulse width.
 

Solved.
PL2303HX revison D is designed as low power and internal pull up resistor on RXD is over 100k and voltage level is max 3.3V refer on PIN 4 VDD_325 . Photo transistor L-53P3C is sensitive to daylight and have any mimimuc current.
RXD is Tri-State, CMOS Input/Output Pad with level shifter. Level and Driving Capability decided by VDD_325 3.3V max.
Fortunately IC have internal 5V to 3.3V LDO with output on Pin 17 VO_33 Regulator Power Output, 3.3V

I add pull up resistor 10k between 3.3V and RXD and on VO_33 add 100nF capacitor because the Chinese manufacturer forgot to install.
 

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