Except it's not quite portable if you also need to carry a power source and look for an outlet, now is it?
Well I decided to fix that:
I used a separate charger board with protection and a step-up module built on fp6291 high frequency pwm DC converter IC. I had to swap the resistor in the feedback divider to 130k (circled on the pic) to bump output voltage from 5v to 8.4v:
Also I modified the main board so that I could use the built in power switch. It was quite easy, just cut two tracks to the switch and add a jumper bypassing the protection diode (we don't want to waste 0.7v there, also bringing the voltage on par with what 9v with a diode would be):
Now to add a bit of thermal glue to stick the modules on the enclosure and add a cut in the bottom panel for the charging port:
Stick the battery pack on the back of the case with some double sided tape and tidy up the wiring to complete the whole thing. I now have an awesome portable scope:
If you want to buy the same things I used here are the links:
- Charging controller (5 of them for dirt cheap): http://www.ebay.com/itm/5pcs-Micro-USB- ... tkn=iOtp8j
- Step-up module: http://www.ebay.com/itm/112064300397?_t ... EBIDX%3AIT
- Battery pack: http://www.ebay.com/itm/3-7V-4000mAh-Li ... SwRgJXlbYJ
I also recommend to recharge early because even though the charge controller has over discharge protection, it's quite low at 2.5v. You shouldn't let your li-ion battery fall below 3.0v, unless it's specifically rated for low discharge.
If you use another step up module, make sure it's switching frequency is high. With the one I used VCC ripple (a few mV at 1mhz) has no noticeable effect on the waveform acquisition because it's much higher than the bandwidth of the scope. With a lower frequency switching module you most likely will have to fight the ripple with some caps and filters.
- Bare li-ion pack hanging out is no bueno, it can get punctured and then it's galaxy s7 all over again. I would like to add some cover for it, ideally a 3d printed one with a backstand.
- Maybe when the firmware sources are released it can be hacked to use one of the unused controller pins to monitor battery voltage, that would be awesome.