Reddit reviews EBL 4-Pack 9V Batteries Li-ion 9 Volt Rechargeable Batteries with 840 9V Battery Charger
We found 4 Reddit comments about EBL 4-Pack 9V Batteries Li-ion 9 Volt Rechargeable Batteries with 840 9V Battery Charger. Here are the top ones, ranked by their Reddit score.
Package: 4 pack rechargeable 9V battery and a 9V rechargeable battery charger.This charger can charge 1~2pcs 9V lithium rechargeable batteries.No memory effect,improved low self discharge makes it still maintain 75% of capacity after 3 year of non-use.Recommended for smoke alarms, professional audio and medical devices.
well it's a pretty shit battery setup so we ain't wrong. If you insist on running a 9V use these: http://www.amazon.com/Battery-Charger-600mAh-Rechargeable-Batteries/dp/B00HV4KFSA since they'll at least give you IMR caliber performance.
I don't really wanna post the code for ethical reasons (I started with some basic Adafruit code for bluetooth and turned it into a full OS). But here's a feature list:
I used u8g2's u8x8 mode for the screen drawing, as it requires no ram.
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Here are my parts:
Voltage regulator (takes 8.4v down to 5v)
22pF capacitors
16MHz Oscillator (required for standalone board)
DIYMall blue OLED
Knockoff Arduino Uno
Adafruit UART-Capable bluetooth module (makes sending data easier)
Spare ATMega 328 processors
Li-Ion" 9V" (8.4v) batteries (rechargeable)
Switches
9V battery clip
Soldering Kit
Elegoo prototyping PCBs
Jumper wires (makes life easier & tidier)
Elegoo Starter Kit (Comes with LEDs, resistors, and buttons)
You are going to be extremely limited in your opamp options using 5V without a boost converter. If you have a 2.5A 5V input at 100% ideal that is 12.5W. You are really not going to get anywhere near 'good' sound with that.
I am old enough to remember boomboxes, and they required at least 6 D-cell 1.5V batteries and ate them up fast. If I were you, I would get some 18650 Li-Ions or flat-packs, good Li-ion charger, and series them up, using a separate charger. With this you can achieve as many 3.7V+3.7V combinations as you have room for, provided you DO NOT attempt to charge them inside the unit. For this you need to buy a dedicated pack with its own charging circuit in it to take USB and not blow up the batteries by leaving some of them at different voltage levels.
You do not want to fuck with Li-Ion charging by yourself, get something pre-made to do it and use that.
How about this:
9V snap connectors at a dime a dozen, put a few in parallel and make a battery indicator. When it gets low, swap out the batteries for charged ones and put the old ones in the charger. Here is an indicator I used for a power drill. Feel free to use it, of course change the zeners to whatever is suited:
You could also do this with 18650s but they are bigger. Do some research but really, using a 5V usb will give very limited results.
EDIT
You can charge them in the device if you have a charger that charges each cell separately. That is what I am doing with the above hack and a tenergy charger. Do not attempt to charge a pack of cells at once without a balance charger or a built in balance charger. This is dangerous and might lead to such minor inconveniences as lack of un-burned down residence and chronic not-being-alive syndrome.
https://www.ikmultimedia.com/products/irigpre/ + https://www.amazon.com/Headphones-Convertors-Headphone-Microphone-Simultaneously/dp/B01M8G1U0C + https://www.amazon.com/EBL-Batteries-Rechargeable-Battery-Charger/dp/B00HV4KFSA
The NTG3 drains out a 450mAH rechargeable 9V in about 5 hours. Read somewhere that the iRig can be damaged by high current batteries but this is yet to be confirmed. My iRig started to present some bad contact in the on/off switch after 2 years of some intense use (2 on/off cycles per working day) so I jump soldered the contacts and now it stays on as long as the battery is in it. I use it on a boom pole before a Sennheiser G3 plug-on TX. Works like a charm.