More power (literally) for the HP-41, follow-up.

[Diego Diaz]

Hi all,

Just to keep track of the progress, here you are some details of this project advances.

Batteries arrived Tue. past week so I can finally build a "rudimentary" (and quite ugly) but functional prototype.

Once confirmed everything fits (tightly) into the battery compartment, back to the PCB drawing sw to design the final layout of the electronics and make sure the dimensions of the boards are as precise as possible to mimic the original battery holder.

Some technical details follows for those who might be interested: (you can jump to the pics in case you're not ;-)

The Power Pack (now officially designated as 82120D) is built using 3 PCB's. The outer (cover) one is 1.6mm thick, it is slotted on the top to allow the removal of the pack in a similar way as the original and sports the "82120D" part number.

On top of it (seeing from the natural position of the calculator), a second board, 0.8mm thick, will be firmly welded by 12 spots; this contains the electronics (USB-C charger, DC/DC converter, the "BAT" annunciator comparator circuit, connection terminals and the insertion safety switch).

Finally a third 0.8mm thick board will carry the LiPo battery itself and one 1Amp fuse. This board will be connected to the electronics board by 6 DuPont header&plugs.

A slot in this board (for the safety switch actuator) prevents it from being inserted the wrong way. However, even if someone manages to connect it to the headers in the opposite direction the the design foresee such circumstance and avoids any reversed voltage to reach the electronics.

The safety switch disconnects the negative terminal of the battery to preserve power when the Pack is not in use. If the user wants to charge the Pack out of the calculator just need to keep the switch pressed: a simple elastic band can do the job.

Last required parts have already been ordered (and shipped according to Mouser's email), and PCB's are in production (according to JLCPCB). Time to wait and see if all these pieces can finally be joined together and we get a new, up to date and reliable power source for our 41's.

All the best from the Caribbean!

Diego.

PS: Yes, there's still time to enjoy the sunny beaches. ;-)