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A simple ESP-01 USB adapter with toggle switch for reprogramming

ESP-01 is a simple ESP8266 module which can be purchased cheaply from Aliexpress. At one of promotion, I purchased an ESP-01 for just S$1.97. That's very cheap for a wifi enabled microcontroller. An ESP-01 can be a WIFI bridge for non-connected microcontroller such as Arduino UNO, Mega, Nano etc. Communication between the microcontroller can be done using the serial link between them.

I have written a post on this using ESP-Link to connect to an Arduino Pro Mini. Together with the client library provided, the Pro Mini can easily transfer sensor data via MQTT.
http://iotdiary.blogspot.sg/2017/09/using-esp-link-transparent-bridge.html

For the most part, once the firmware is in place, normally I will use OTA to update. Sometimes, I wanted to reuse the same controller for another firmware and I have rewired up the controller for reflashing. This makes it very inconvenient to use.

Recently, I bought a USB ESP-01 adapter thinking that my problem is solved. When I received it and realised that it is cannot be a programmer so I decided to wire up a toggle switch.

The GPIO0 is wired to the centre pin and one of the pins is pulled up to VCC (Normal Operation) and the other pin is wired to ground (Programming Mode).
After some soldering and covering the exposed parts using a glue gun, the final output looks like this. Not very nice but workable. 
Instead of soldering and glueing, you can also purchase an adapter with the toggle switch. The price difference is about S$2-$3 compared to those without.

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