AC supply to digital output

Question

I need to sample 8 power switches connected to 230 Volt supply. I want to record the status of these switch every 10 seconds and send to cloud for which I am using arduino with ethernet shield.

For example if status of switches is as below

On Off on On Off Off Off Off

then output should be a single byte 10110000.

I am a novice in electronic so bare with me if its quite straight forward.

As i want this circuit to be place in box for switch space is a concern.

Also my digital pins on Arduino are already used for other purposes.

One option which I was thinking was to use 8 differnt LM7805 to convert AC to dc from all switches and then use some D to A converter, and feed back this Analog signal to analog pin of Arduino from where I can convert that to byte and send to web.

Please guide if LM7805 will take 220V supply (home supply in India) and if not how that can be managed. Also I think using 8 LM7805 will take lot of space.

Answer 1

No. You definitely can not use LM7805 regulators for this task.

• They are low-voltage DC regulators. They expect, typically, 8 - 20 V DC in.
• YOU NEED ELECTRICAL ISOLATION between the mains and your Arduino. The isolation should be rated to at least 1,000 V.

You need to either use a 230 V relay to monitor each switch or use an opto-isolator with mains dropping resistors. The relay is the safer option in your case. Mount the relays securely and keep all mains wiring away from the Arduino wiring.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 1. Relay signalling of mains voltage.

In this configuration inputs are pulled 'low'. You need to configure internal pull-up resistors in the Arduino.

Judging by your question you have limited knowledge about electricity so I urge extreme caution.