replacement for a NDP6020P. They stopped making them. How do you find an alternative?

Hi,

You might want to share the circuit that you plan to use this device with. It's up to you if you wish to do so, but if it is a hobby circuit from the Internet, it may well not be ideal (there can be better ways to achieve things). RIght now I don't know either way, maybe it actually is the perfect ideal part, but I have no idea, and just from being an overly suspicious person usually!, I'd be wanting to examine the circuit if it were me.

this is what I'm doing. It needs to have a button large enough for a service dog to press and require as little charging as possible. This should shut off 10-15 seconds after pressing. It sends a message to home assistant for emergency alerts. I am very new to electronics (less then a year). so I don't know if this will work till breadboard.

Good point. The wemos board will be inside a case. so no one will be able to connect the wemos usb into anything. But now I wonder if the 1904 will do the job. You are right a lot more thinking. The bat only has 3.7v and min power for the wemos is 3.3. that might be to close. Maybe I need a 9v and convert it to 5v. then just change it every year. I just hate to waist.

I don't think cutting the trace on the board and patching in a pin is something I can do. But I do get what your doing. The wemo will be inside a case and I'm the user. well me and the dog are so that shouldn't be problem, but I think I might be short on power after reading your last post. bat is 3.7 and min for wemos is 3.3. I think i have to rethink a few things.

Ok now i get what "add an NPN/NFET in parallel with the pushbutton" from Scottiebabe means. very clever I would have never thought of that.

Three AA cells would get you to around 4-4.5V, which if connected to VUSB (i.e. if you are certain no-one will plug in the USB connector while the AA cells are connected) would easily last a year or longer, there's no need for the LiPo charger then.

If the AA cell holder was mounted in front of the USB port, i.e. you have to physically disconnect the AA cell holder to move it out of the way to plug in the USB connector, then that would solve the problem.

I recently did something kind of similar, where I just stuck a microswitch with lever, in front of a USB port. The lever is physically in the way of the USB port. The user cannot plug in a USB plug, without pushing down on the microswitch first. The microswitch cuts the power from the battery.

Kind of an ugly solution, but it solved the problem.

You can apply anything from about 3.4V upward to the VUSB pin (i.e. the pin labelled 5V on your diagram) on the Wemos board, it will regulate it down to 3.3V, so three AA cells will do the job (provided you're sure the USB connector won't be plugged in while the AA cells are connected).

I think your doing a great job and working on a really neat project! Your line of thinking is totally correct. After the MCU sets D1 high and turns itself off there are some protection diodes in the chip that may not allow for D1 pin to get pulled up to vbat.

So, the mcu may never get fully turned off. The schematic shabaz sketched out, shows the additional NPN. This way for the MCU to turn itself off, its sets D1 Low, which is also an allowable IO pin voltage when the power is removed.  

I cant wait for the parts to get here so i can breadboard this. I want to try it both ways and see what happens. I will let everyone know. In the mean time I need to learn how to pick the right parts. like if I designed this myself how would I know what mosfet and npn to pick.

FET:

choose a voltage range - anything over 6 V for you, which is any FET

choose a gate threshold voltage - anything less than 3V  for you

choose a max current - anything over 100 mA for you, which is pretty much any FET

choose a package - TO92 for though hole TP2104N3-G  , SOT23 for SMT BSS306NH6327XTSA1

You may need to limit the voltage going to D1

ok i tried to add the npn in parallel with the switch but i couldn't get it to work. so i went back to my original schematic and added a tp4056. i haven't tested the bat yet but at least i can get it to work, now. I kind of feel like i failed because i couldn't get the npn to work

well that went up in flames. i will be starting over. but now i have to add sound and leds..

well that went up in flames. i will be starting over. but now i have to add sound and leds..