Pulse stretcher using CMOS 4000 series for detecting data for MAX232 in serial com

[D.A.(Tony)Stewart]

So you want to toggle with continuous data but at a lower rate and not load the signal. But still stretch short bursts.

One way to define this is go on for 1/2 s and off for same if continued then repeat.
Using same RS232 to CMOS inverter and diode cap RC retriggerable one shot as my 1st answer then add a gated NAND Schmitt trigger 1Hz
Oscillator.

For an Monostable and astable in one chip use the HCMOS dual 1 shot IC, 74HC221 or equiv. then choose correct plarity and trigger both to start with start bit and 2nd to timeout oscillating at 1 Hz after 1st goes low.

 

[BradtheRad]

I just realized that for serial port (232) working at 9600 baud, 8 data bits, no parity and 1-stop bit which is where i intend to use this circuit would be an equivalent to 4800 Hz. In order for the human eyes to perceive the train pulse would require to lower the frequency to at least 12 Hz.

I had to deal with this after getting my first Macintosh. I wanted to transfer all my programs from my VIC-20 and 64 computers.

They had baud rates of 300 back then. Just slow enough to be possible (though not easy) for me to watch the waveforms on my scope.

Can you select 300 baud for your transfer rate? The same rate has to be set on both the sending and receiving devices.

 

[SparkyChem]

So you want to toggle with continuous data but at a lower rate and not load the signal. But still stretch short bursts.

One way to define this is go on for 1/2 s and off for same if continued then repeat.
Using same RS232 to CMOS inverter and diode cap RC retriggerable one shot as my 1st answer then add a gated NAND Schmitt trigger 1Hz
Oscillator.

For an Monostable and astable in one chip use the HCMOS dual 1 shot IC, 74HC221 or equiv. then choose correct plarity and trigger both to start with start bit and 2nd to timeout oscillating at 1 Hz after 1st goes low.

Okay understood, maybe i'm asking too much, but can you post a circuit to accompany your explanation?. Just to be sure my interpretation is not different from yours. i'm thinking to use a 4011.

I don't know much about the 74HC221 you mentioned, can you please post an example of how to use it?. i tried to search about it but i couldn't find a clear application.

I had to deal with this after getting my first Macintosh. I wanted to transfer all my programs from my VIC-20 and 64 computers.

They had baud rates of 300 back then. Just slow enough to be possible (though not easy) for me to watch the waveforms on my scope.

Can you select 300 baud for your transfer rate? The same rate has to be set on both the sending and receiving devices.

I also have fond memories of classic Mac years but they were not available to me at the time. So pity. Unfortunately i cannot go as low like 300 baud. I have to stick with 9600 for my application.