how to generate anlog voltages programable by micro 8051

[anan1975]

hi
in my project o have to generate 0-5 volts programmable at 6 places how it is possible.better to use 8 adcs or pwm routines in 8051 microcontroller suggest with the minimum hardware.

Anand

 

[svhb]

depends on what fequencies you need to generate with the analog signals. If it is for low frequencies or setpoints, the PWM solutions will be lowest cost (one R-C filter per output).

The maximum frequency you can generate with the PWM solution depends on how fast you can toggle the pin, and the residual ripple you can allow on the output signal of the filter. However, you can reduce the output ripple by using a second order RC-filter.

 

[IanP]

One other option is to use (purely) resitor-ladder .. see attached picture ..

https://en.wikipedia.org/wiki/Resistor_ladder

8051 MCU has several pins that can be used for that purpose (with fixed external pull-ups), so the number of bits in this DAC is only limited by the number of available pins ..


Rgds,
IanP

 

[svhb]

Or you can even combine both things, few pins on a resistor ladder and toggle between two output values (add a capacitor on the output). This way you interpolate between the two values applied to the outputs.

For a very expert-solution, you can also exploit the fact that you have 3 possible states at the output pin of the micro controller (1, 0 and high-Z). This can reduce the ripple on the output of a pwm-solution.

TO reduce the ripple, you can also use a technique described here: **broken link removed**
It is targeted to digital logic, I don't know how easy it is to program this into a micro controller (speed?)

Stefaan

 

[anan1975]

but the problem occurs when micro is busy in doing other task then pwm distrubes the output. Please suggest the hardware where once micro feed the data it will latch analog op upto next change.

 

[svhb]

It really all depends on what the bandwidth is of the signal to generate.

If it is very low (few Hz), you can probably use an interrupt routine triggered by a timer.