The first read from the device after it has been switched on will return 0x80 and will also trigger the new sample from channel 0. If you read it a second time, it will return the sample previously read and generate a fresh sample. Each reading will be an 8-bit value (ranging from 0 to 255), representing the voltage to VCC (in this case, 0 V to 3.3 V). On the www.dx.com module, channel 0 is connected to a light sensor, so if you cover up the module with your hand and resend the command, you will observe a change in the values (darker means a higher value and lighter means a lower one). You will find that the readings are always one behind; this is because, as it returns the previous sample, it captures the next sample.
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