Controlling a digital potentiometer through the seriallport

[iver89]

Hi! I want to controll a digital pontetiometer from my seriallport. The potentiometer is DS1804 from Maxim (datasheet). How do I make a signal go high or low, and what do it actually mean? I'm not a superprogrammer, but I know some Pascal.

Anyone?

 

[kinjalgp]

You cannot connect serial port directly to your potentiometer. Thats because serial port operates at +-12V which will blow up your potentiometer. You first need to convert this RS232 signals to TTL using level shifter ICs like MAX232.

Also you can't send data to potentiometer using its TXD pin because the speed of transmission is fixed for this pin depending on baud rate and you have no control over individual bits to be sent. Instead you can use other signals like RTS and make it high/low (1 and 0) with required speed.

 

[Exo]

Use the parallel port. Parallel port allows you to control lines indepently, making then high (5V) of low(0V).

A start on how to program the parallel port
**broken link removed**

 

[iver89]

what is actually a high or low signal? is it 5V (high) and 0V (low) as Exo said?

 

[Exo]

Well, it depends.

A high means a logic '1' ; and low means logic '0'.
However how this is implemented in hardware depends on how the designers choose to do it...

TTL signals for example (the ones you need to control the digital pot, and the same signals the pc parallel port uses) use a 0V to indicate low; and 5V to indicate high.

RS232 signals (the serial pc port) use approx. +12V to indicate a high and -12V to indicate low.

 

[iver89]

tnx Exo! so, that means that if I use a MAX232, I still can use the seriallport?

 

[Exo]

I think you better use the parallel port. The parallel port allows you to manually set a certain output high or low in software, wich is what you need to drive the digital pot.
A serial port however was only designed to send data between PC's or modems. The data sent by a serial port is 'encoded' in a specific way, and you need an UART to decode it; if you use the parallel port you can probabely hook it to the digital pot directly.

 

[kinjalgp]

A serial port however was only designed to send data between PC's or modems. The data sent by a serial port is 'encoded' in a specific way, and you need an UART to decode it

Not necessarily. If you are using RXD and TXD pins then only you require UARTs to decode data. While you can use rest other control signals as individual digital output pins and you can pull it low or high using software. One such pin is RTS.