DAC Of PIC(18F458)

• What is ADC ? -In electronics, a digital-to-analog converter (DAC, D/A, D2A or D-to-A) is a function that converts digital data (usually binary) into ananalog signal (current, voltage, or electric charge).

• How DAC work – Digital-to-analog conversion is a process exactly the reverse of ADC (analog to digital converter) in which signals having a few (usually two) defined levels or states (digital) we can also say impulses are converted into signals having a theoretically infinite number of states (analog) or continuous. A common example is the processing, by a modem,of computer data into audio-frequency (AF) tones that can be transmitted over a twisted pair telephone line. The circuit that performs this function is a digital-to-analog converter (DAC).

• About DAC– two methods are used to convert digital data into the analog form, weighted register method and R/2R ladder method. here we use 8-bit DAC called MC1408 (DAC 0808) which uses weighted register method and is efficient. DAC resolution is decided by no of bit input. Analog output maximum is equal to , where n = no of input bits. So DAC 0808 has  discrete voltage or current values. DAC0808 converts digital data in current

Iref generally set to 2.0 mA at pin 14

So output current (Iout), we have to convert this current in voltage and we will do it through applying load. Iref current output is isolated by connecting it to an opamp such as 741 with 5K of feedback resister

For example – R=5K and Iref = 2 mA calculate Vout for 10011001 (99H)

Iout = 2 mA (153 / 256) =1.195 mA

Vout = 1.195 mA x 5 K = 5.975 V

• Applications – DACs are commonly used in music players to convert digital data streams into analog audio signals. They are also used in televisions and mobile phones to convert digital video data into analog video signals which connect to the screen drivers to display monochrome or color images

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