small serial port project, and hello from a new member :)

[izua]

hey guys!

i've been an amateur electronist for a while (working with a few ics, such as counters, and gates, but not all of them) and for a few days, i'm having this idea of using my programming skills in relation with my *few* electronic skills.
more exactly, i want to make a simple digital clock, controlled by the computer (or perhaps, a numerical display is a more adequate name).

i don't know exactly how should i do it. i believe i'll send a clock pulse from the computer, and 4 bits fed into a cmos 4511 (bcd to 7segment translator) ?
but how do i exactly send those 4 bits? does the serial port implementation allows for 5 bits at once (clock + 4 bits)?

or i should send the clock + another bit (i believe i can send at least two bits, right? ), and the circuit will count? like, first 4 bits go to the first 7-segment display, the second 4 (4-8) go to the second display? i believe the way our eyes perceive the flashing light will actually fake me into seeing the 4 digits lit up at all time.

i was also thinking if it's not better to send instead 7 bits. for a total of 4 digits, results 28 hertz per one full iteration of each segment, thus, perhaps a 50 hz "flash" rate will show it up as "permanent lit" (same effect of perceivment). so that's about 1,5khz, will the serial port support it?

thanks everyone - also, if anyone has any idea or suggestion, let me know.
regards,
izua

 

[kannan.k]

Re: small serial port project, and hello from a new member :

Hi Izua

welcome to EDA board.

Regarding your project you could use the parallel port. The parallel port has 8 data lines and 5(if i am not wrong) control lines. You could use them to send the pulses you require. the advantage is that you have a lot of pins at your disposal
programming is also easy.

have fun

kannan.k

 

[budhy]

Re: small serial port project, and hello from a new member :

Regarding your project you could use the parallel port.

Please take a look at
https://www.beyondlogic.org
for Parallel Port Interfacing and Serial Port Interfacing basic

 

[izua]

thanks for the welcome

Hmm. paralel port does sound better, but the cable is really big (and i do have a printer installed on it, i can remove it, anyways).

I don't think control lines are so important (now), since all I need is a clock signal, right?
next thing - if i'll send 8 bits to each 7-segment display via some muxing (thus controlling the individual segment of each), i suppose i will need some kind of amplification or buffering between the led-resitor groups and the actual port, right? or i can drive leds directly from the port?

izua.

 

[kannan.k]

Re: small serial port project, and hello from a new member :

Hi Izua

You would definetly need buffer ICs for the interfacing. The LPT port cannot give current more than a few milli amps. So it cannot drive the 7seg leds direct.
You can connect the bcd to 7seg converter( 4 pins) and use a 3 to 8 demux or 4 to 16 demux to do the scanning of the 7 segments.
in any case the 8 digital outputs can be comfortable.

Please be very carefull with the current drawn/sunk from/to the parallel port. Over current can easily kill it! and if it is inbuilt the motherboard could also be damaged. Using a parallel port addon card would be a safe bet :!: either way you will have to use the buffer ICs and the current drivers.

cheers
kannan.k

this site might be the one you want

http://www.epanorama.net/circuits/parallel_output.html

 

[izua]

Re: small serial port project, and hello from a new member :

Hi Izua

You would definetly need buffer ICs for the interfacing. The LPT port cannot give current more than a few milli amps. So it cannot drive the 7seg leds direct.
You can connect the bcd to 7seg converter( 4 pins) and use a 3 to 8 demux or 4 to 16 demux to do the scanning of the 7 segments.
in any case the 8 digital outputs can be comfortable.

Please be very carefull with the current drawn/sunk from/to the parallel port. Over current can easily kill it! and if it is inbuilt the motherboard could also be damaged. Using a parallel port addon card would be a safe bet :!: either way you will have to use the buffer ICs and the current drivers.

cheers
kannan.k

this site might be the one you want

https://www.epanorama.net/circuits/parallel_output.html

what about optocouplers? i have a few ltv 847s lying around.
i can drive the output of each output pin, by connecting, each opto-led via a resistor to one pin and port ground;
also drive each input pin by connecting each opto-transistor between v+ and ground, and a pulldown resistor, so when i'll switch an opto-led on, the respective optotransistor will switch on, driving a pin to 1, otherwise, the pulldown will set the pin to 0.

this will be applied to all pins. is it safer?
can it be damaged if all pins will be set to 1?

thanks.

edit: i do suck at explaining, so i made a drawing.
**broken link removed**
um, yeah, and i'm not that good at drawing, either

 

[kannan.k]

Re: small serial port project, and hello from a new member :

Hi

The optocouplers would also be a better option. I not sure which pin you are reffering to

can it be damaged if all pins will be set to 1?

i presume you are asking if the voltage level in a LPT port is pulled low and using software we set it to one will there be any damage to the port? It wont be damaged if the pullup/pulldown resistors are of the correct value. actually this is the procedure to get the input from port pin (we use this in 8051 microcontrollers)

Also the opto couplers need fair amount of current to drive the LED. Check with your datasheet to see if the current is within limits. or you might have to go for a different optocoupler.

And BTW the picture was helpful ^_^
cheers
kannan.k

 

[Kuzito]

Re: small serial port project, and hello from a new member :

Hi and excuse fo my bad english,

I try to run similar project including PIC16F874 , MAX232 RS to TTL convertor and simple software to control 8 outputs with relays.

**broken link removed**

I send via Windows Terminal or this software one bait to PIC and when PIC receives execute turn ON or turn OFF definite output.

I test using MAX232 convertor and all work fines. I test rates from 1200 to 115200 and no have any problems.

Now I buy 433 MHz receiver and transmiter to make wireless but without success.
When I connect direct OUTPUT TTL convertor to PIC work, when using wireless – no. I test with baud=1200 – the same.

**broken link removed**

Thanks everyone for any suggestion

Regards
Kuzito

 

[izua]

Re: small serial port project, and hello from a new member :

well, i almost finished it.
problem is that i'l either use a very big copper-textolite board, or i'll use some writing-tool with a smaller resolution.

some guy suggested me using dilutted tar and an old pen (fountainless, you know, the old type, that you sink in a inkbottle every few words).
i've tried using an OHP marker, but that's really cr*p.

here's my schematic, using milimetric paper, i was able to draw a pcb for it in 12x12 cm. the biggest disance between traces is about 5 mm, which is not really great, since my current marker has a resolution of about 2mm.

**broken link removed**

any suggestions?

um, yeah, there's also a drawing mistake. the left chip should have pins 1 connected to v+, 3 to where 1 is now, 5 to 3, and 7 to 5. i just made a line longer