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magicChristian 1 hour ago
The main goal for a new charger should be a universal charger for all common battery chemistry (Lipo, NiMH but also NiCd and Lead acid). To be usable as a power supply woul be a nice feature. To control current and to monitor voltage it is necessary to have a multichannel ADC and a microcontroller. Because of low speed requirement a raspi is not necessary;   an ARM  M3 would be a good choice.  The maximum voltage should be 18 V to cover  4S LiPo and 6 cell Lead Acid. The maximum current maybe  1 Amp and at least 4 places for AA or AAA cells. The voltage resolution should be better then  50mV which is easily done by 10 bit ADC. One problem is charging LiPo cells in a serial configuration - the only correct way needs contact to all nodes between cells (there are special IC´s for that purpoe available). I am looking forward to this project and would like to be a meber of the team.
Battery Charger Next Generation: request for comments
HaSch 3 hours ago
The level shifter around BSS138 is not working for me, Neopixel LEDs remains dark. Are there different BSs138 types in the market? Maybe it will work with another brand of BSS138 or another MOSFET. What other actions could bring the circuit to life?
ESP8266 web server for Neopixel LED strips [160487]
ClemensValens 1 day ago
Are you aware of the fact that the kind of pushbuttons shown in the photograph is typically rated for only 50 mA @ 24 V? In your circuit it has to pass the full (inrush) current to the Arduino, so you might want to choose a more suitable type. I modified the circuit to move the switch out of the power path, see V5 (attached). I added an LED too.
On/Off Button for Arduino; switching off software controlled
ClemensValens 1 day ago
Looking once more at V3 I think an extra diode is needed to prevent voltage inversion passing through the body diode of Q1. See D1 in attached V4.
On/Off Button for Arduino; switching off software controlled
Sarbjit Singh Mal
Sarbjit Singh Mal 2 days ago
As per the circuit description,  voltage across Capacitor C15 will never go above VBE(sat)  i.e. Base to Emitter saturation voltage ( 1.0V) of transistors T7 & T8 (when Base to Emitter  diode will get forward bias) in case of positive  DC offset voltage more than  0.55 V ( for T8) or a negative DC offset greater than 0.85 V (for T7) at the output and almost entire offset voltage (less  1.0V VBE(sat)  of T7/T8) will appear across R23 (15kΩ) and current through R23 will be limited to approx. 3.67 mA { i.e. (56-1.0)/15000} in case of DC offset voltage swing to even up to +V or –V supply rail. Capacitor C15 is already shown as non-polar in the circuit schematic. Mal  
Q-Watt - Simple Audio Power Amplifier (110656)