DIY power supply for J720 or MP900c

I built these for my J720 with the 12v 4.8mm plug and my mp900c with 12v 4.0mm plug, both use a cell phone usb cable with a 2.0 amp cell phone charger 5v soldered to a dc to dc adjustable inverter that steps up voltage from 5v to 12v (you can adjust it). They work great, can be used with any of those higher power cell charger 2.0 amp or more cell phone chargers. Instead of dragging multiple different brick type chargers, you can use the same charger for both hpc's using different usb mod cables. Cost less than 8-10 bucks I think, ...even less if you have spare cell phone chargers around( (I need to 3D print a case for the inverter, or enclose it). Compare that to $24 on Amazon for the MP900c charger. Way more convenient for travel, etc.

Instructions to follow later and cost estimate options...(and verify dc polarity...center pin is positive +... before use if you jump into)

Edited by joval 2019-06-11 4:21 PM






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USB12VCHARGER_mod.jpg (46KB - 0 downloads)

That is very cool!

What parts do people need. Is the PCB pre-fab or did you make it?

This should clue you in...they are cheap and come preassembled...I bought multiples because I needed several for my multiple j720 and mp900c's. Voltage must be adjusted with voltmeter (I will look into other options and give more details later)

Oh I see, so turn the screw to adjust the output voltage. Quaint.

My problem is that I don't have any of the DC connectors for the Jornada. I don't suppose you happen to have worked out which connector it uses?

As I mentioned in the first line of this thread the J720 uses the 4.8mm diameter plug found here as noted on my second post:

Whereas the MP900c works with a 4.0mm diameter plug also noted above (I guess I had them in reverse order) found here: .

USB cable? I use old ones or can buy one at a "dollar store" for, well, one Dollar. When I get around to it I will post some photos on how to cut off the micro-usb end and attach the barrel plugs and how to/where to cut off the usb2.0 plug and splice in the dc inverter.

Hmmm...for some reason I can't seem to edit my previous posts (damn those Rooskies!)

No, I meant that they must have a standards part number. It must be a thing.

To do the Amazon things, hit reply (instead of using the quick reply) and you'll find the Amazon button in the toolbar

here is a simple option, just cut cable and splice in the inverter...cheap but arrives by slow boat from china :

https://www.ebay.com/itm/USB-A-to-DC-plug-4-0mm-1-7mm-Power-Adapter-...

This is really cool and right up my alley as an formally untrained electronics enthusiast Jornada and MP900 user.

I just realized that these USB powered inverter to barrel plug adapters will make it possible to recharge your HPC from a portable usb cell phone battery pack. Jornada batteries are probably available somewhere, but who can beat having a battery pack that you can use on your cell phone and J720 or MP900c as well...great for backup.

I have found the above 2 amp 5volt phone wall outlet chargers when combined with the 2 amp inverter shown above is a bit on the weak side when both charging and using the MP900c simultaneously...the solution is to turn the MP900c off if the battery is really low. Once charged up, these will power the 900c for continuous use as a Date/Time/Day of the Week Clock with no problem, as an example.

Lastly, there is an even simpler usb to hpc power inverter to build...it uses an inverter with a micro usb that accepts a regular cell phone charge cord...you only have to solder 2 wires from the barrel plug leads to it (always check the polarity). I will post details later.



Edited by joval 2019-06-16 5:21 AM

I was having a further look at this. I think these are what we want aren't they?

5v to 12v in-line cable with 1.7x4.0mm jacks for the HP Jornada 710, 720, 728, MobilePro 900, 900C.

They're calling them for use on the Echo Spot and Echo Dot.

DigitCont USB 5V to DC 12V Power Cable, Compatible with Amazon Echo Spot and Echo Dot 3rd Generation, USB Voltage Step Up Converter Cable, Power Supply Adapter Cable, DC 5V to DC 12V Cable (Black) -

DigitCont USB 5V to DC 12V Power Cable, Compatible with Amazon Echo Spot and Echo Dot 3rd Generation, USB Voltage Step Up Converter Cable, Power Supply Adapter Cable, DC 5V to DC 12V Cable,1 ft,Black -

Great, a good option for those that are not DIY oriented, but that option is a bit pricey...you can build our own for 1/3 that price and have them all over the house to run date/time clocks, or dedicated webcontroller clients, etc. I have quite a number of J720 and 3 MP900c...and so I needed quite a few as I only had chargers for one of each. That plug size is a little small for the J720 (it uses a 4.8mm plug), but I just checked and it does work at 4.0mm too).

How nice to discover all these alternatives for charging.

True, but for those who aren't equipped with a soldering iron or don't want to have to buy parts for 10 to get one cable, a pre-fab option makes sense.

I can make them, but I don't really want to have to buy 10 DC jacks etc as I only have to store them and am unlikely to ever use them. I don't think that I have any old USB leads to cannibalise either.

Agree...more versatile and cheaper than OEM charger...so...a good find on your part. So much for my patent options...

Do it with the step-up circuit integrated into the USB connector and get rid of the bump; and patent that

Nice set of solutions - thanks for adding the detail about which plug the MP900 uses. I found a plug that fit at my local electronic junk store for $1 so simply grafted that wire onto the wire of an extra 12v 1.2a adapter and it seems to work to both power and charge the device. The original MP 900 charger is 12v, 2a.