Wifi and Boost Converter

A project log for Data Collection Terminal

General purpose low cost handheld terminal with screen/kbd, wifi, barcode and RFID reader for industrial or commercial (or any other) use

BozBoz 11/29/2014 at 09:090 Comments

After several days of cussing and pulling out hair I have finally figured the problem with the power and wifi.

The NCP1421 works OK but cannot handle the sudden load of 250mA+ put on it by the ESP8266 wifi quick enough to prevent a brown out on the other parts of the circuit. As I will be switching power off and on the ESP8266 every time this is a problem. I tried putting capacitors on the Vcc up to 1500uf but it was getting a bit ridiculous so I thought I would try and stop the brown out by isolating the CPU/LCD 3.3V behind a diode (D1)/capacitor (c6) which will charge and buffer Vcc (PIC+LCD=24mA when not in sleep) and when the sudden drop occurs the schottky diode (d1) will not conduct and (hopefully and with careful selection) C6 will hold Vcc for the few milliseconds until the power stabilises.

As this is more a hack than a design I have also reverted to an old design using a LiPo 3.7V cell, both boards will be produced simultaneously so I can work a bit quicker as its getting toward XMAS I've updated the details on my website here