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2.6.2. Generating a Stair Step Voltage from DAC

In this lesson we are like to design, how to generate stair step voltage from 0volt trough 5 volt, with resolution 1 volt each step. There is something you must to do is to calculate the konstanta K, as you have learned in previous lesson.

Step 1st
Build the circuit as shown in figure 2.6.2. As you seen on figure 2.6.2. P0.0 trough P0.7 is connected to A8 - A1.
or example, we assumes that the Vref = 5 volt, R14 = 5 k, and Rf = 5k

   K = Vref/ R14;
     = 5/5k
     = 1 mA
If, we put logic high into A1 through A8 then we have:
   Io = 1 mA x 0.99
      = 1 mA
So,Vo = Io x Rf
      = 1 mA x 5k
      = 5 volt
Voltage Resolution = 5/255 = 0.02 volt

* Voltage 0 volt
      = 0/ 0.02
      = 0 decimal 
* Voltage 1 volt
      = 1/0.02
      = 50 decimal
 * Voltage 2 volt
      = 2/0.02
      = 100 decimal
* Voltage 3 volt
      = 3/0.02
      = 150 decimal
* Voltage 4 volt
      = 4/0.02
      = 200 decimal
* Voltage 5 volt
      = 5/0.02
      = 255 decimal

Step 2nd
In this step, you must tipe the assembly program to make a voltage from your DAC, we assume that you have already known the editor, we used MIDE-51 to edit the program. ( Download File asm : exp262.zip, Download Complete Circuit File : DAC0808.pdf )

        org 0h
start: mov A,#0
       mov P0,A
       call delay
;
       mov A,#50
       mov P0,A
       call delay
;
       mov A,#100
       mov P0,A
       call delay
;
       mov A,#150
       mov P0,A
       call delay
;
       mov A,#200
       mov P0,A
       call delay
;
       mov A,#255
       mov P0,A
       call delay
;  
       sjmp start
;=============================================
;subroutine delay created to rise delay time
;=============================================
delay: mov R1,#255
del1:  mov R2,#255
del2:  djnz R2,del2
       djnz R1,del1
       ret
end

Step 3rd
Safe your assembly program above, and name it with dac2.asm (for example) Compile the program that you have been save by using MIDE-51, see the software instruction.

Step 4th
Download your hex file into the microcontroller by using Microcontroller ATMEL ISP software, see the instruction.After download this hex file you'll see the action of DAC ( of course if your cable connection and your program are corrected )

Comments, questions and discussion about this topic

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