Schematic Design

The purpose of the schematic design is to organize the design elements in a way that is clear and easy to follow.  The schematic is used to show the electrical connections between components in a circuit.


I opened the schematic.

I placed the ESP-12A and noted the power connections Vcc and GND.  This device requires 3.3 volts operational voltage so I will need a voltage regulator to supply the radio. While looking for more data concerning the  ESP -12E I found a better pin layout and description on ESP8266.com.  On line I have found the part draws 300 mA at peak.

Searching on Digikey, I found a regulator AZ1117CH-3.3 under US $0.09 each in quantities of 4000.  It looked like a very good fit until I looked at dropout voltage.  With a 3.7 V lithium battery for the supply, a dropout voltage greater than 0.4V is too much. Typical dropout voltage for this part is 1.2V.

Note: Dropout voltage is the minimum extra voltage above regulated to maintain regulation. I 3.3V regulator with a 0.5V dropout voltage requires an input voltage of 3.3+0.5 = 3.8V to still be able to regulate to 3.3 Volts.

So I look again, I have used and like the AP7333-33 voltage regulator.  It’s maximum current is 300 mA.  that doesn’t leave any margin.  I keep looking. The next part I find from Digikey is the AP2112K-3.3. It can run at up to 600mA leaving plenty of margin, with a dropout voltage of 0.25 V. The price is under US$0.11 each in quantities of 3000.

I add that to my library and to the schematic. I found a similar SOT23-5 pin part exported it. I then imported it in the the programmer library and edited the part name to match the ordering number.

Schematic 06062015

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