View source for A7.8051 Interfacing ADC: LDR ← A7.8051 Interfacing ADC: LDR

[[Category:8051 tutorials]]
In this tutorial, we are going to discuss the interfacing of external ADC0808/9 with 8051.<br>
We will be reading the ADC values from channel Zero and transmitted on UART at 9600 baudrate.
[[FILE:ADC.gif]]
<br><br>



=ADC-0808/9 =
8051 does not have the  inbuilt ADC and we will be using the external 8-bit ADC ie. ADC0808/ADC0809.
ADC0809 is an 8-bit Successive Approximation ADC which is multiplexed among 8 input pins.<br>
The A/D module has high and low-voltage reference input that can be set using the pins Vref+ and Vref- as shown in the below image.
With 5v as the Vref+ and 0v as Vref- the resolution of ADC0809 can be determined as below: 
$$resolution of ADC = ((Vref+)  - (Vref-))/(2^{8}-1) = 5/255 =0.0196 = 19.6mv$$
[[File:ADC0809.png]]

===ADC Pins===
Lets see the pins of the ADC0809
*<b>Addres Lines(A,B,C):</b> As mentioned earlier, ADC0809 has 8-muliplexed ADC channels. A particular input channel is selected by using these address bits as shown below.
{| class="table table-striped table-hover table-condensed table-bordered"
|-class="info"
!C || B || A || Selected ADC channel
|-
|0 || 0 || 0 || INO
|-        
|0 || 0 || 1 || IN1
|-        
|0 || 1 || 0 || IN2
|-        
|0 || 1 || 1 || IN3
|-             
|1 || 0 || 0 || IN4
|-        
|1 || 0 || 1 || IN5
|-        
|1 || 1 || 0 || IN6
|-          
|1 || 1 || 1 || IN7
|}<br><br>

*<b>Address Latch Enable (ALE):</b> A low-to-high signal at this pin will latch the above-selected address and selected the respective channel for ADC conversion.
*<b>START Conversion (SOC):</b> The A/D converter’s successive approximation register (SAR) is reset on the positive edge of the start conversion (SC) pulse. Thus we need to generate a LOW-HIGH-LOW pulse for starting the ADC conversion.
*<b>End of Conversion (EOC):</b> Once the conversion is over, this pin is pulled HIGH by ADC0809. This pin needs to be monitored for the conversion to complete and then read the data.
*<b>Output Enable(OE):</b> ADC0809 does the adc conversion and holds the data in the internal registers. A HIGH signal on this pin will bring the data on the output lines.
[[File:Adc0809 TimingDiagram.png]]

=Pin Connections=
You can connect the ADC0809 to any of the PORT pins available on your boards and update this section accordingly.
<html><script src="https://gist.github.com/SaheblalBagwan/dd0169a1f593236a66a0575ac3bd5ba2.js"></script></html>

=Steps for ADC Conversion=
#Select the required ADC channel using A,B,C pins.
#Send a HIGH pulse on ALE for latching the above selected channel.
#Send a HIGH pulse on Start pin to reset the SAR(Successive Approximation Register).
#Pull the ALE line low as the address is lateched and futher changes on A,B,C should not change the channel.
#Pull Start line LOW to start the conversion.
#Wait for the EOC line go HIGH.
#Pull the OE line HIGH to bring the conversion data on DataBus.
#Read the ADC data and pull OE line back to LOW.
#Use the ADC data for further processing
<html><script src="https://gist.github.com/SaheblalBagwan/d47bf4d9abfb1c43a9571e7af9d58000.js"></script></html>

<br>

=Hardware Connection=
[[File:Adc0809 Interafce.png]]
<br><br>

=Code=
Below is the sample code to read the ADC value of channel0 and send it to P0 where the LED's are connected<br>
<html>
<script src="https://gist.github.com/SaheblalBagwan/328e438db789f5e73b74603733207fd6.js"></script></script>
</html>

=Using ExploreEmbedded Libraries=
Below is the sample code to read the ADC value of channel0 and send it on UART at 9600 baud rate.
<html>
<script src="https://gist.github.com/SaheblalBagwan/45353c7008277f68204abfe09ba7fc7a.js"></script>
</html>

[[File:Pic16f877aADC01.PNG]]<br><br>

=Downloads=
Download the complete project folder from the below link:<br>
[https://github.com/ExploreEmbedded/8051_DevelopmentBoard Hardware design Files and Code Library]


Have an opinion, suggestion , question or feedback about the article let it out here!
{{DISQUS}}