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Free Designs

This page has some free designs for you do download and play with as you see fit.

Please note that as usual, you use the designs and information entirely at your own risk.  If you are not willing to accept this, simply don't use the designs.

No support is offered for these designs other than the instructions here. 

Hopefully there will be enough info. for you to fill in any gaps with your skill and creativity.


PRP Series Battery Case

Philips / Simoco PRP series hand held radio: Battery Pack Replacement.

NOTE: if you build this do not charge up the  project battery pack using the original PRP battery charger.  The OEM charger was not built to recharge Li-ion batteries as they weren't in general use or even maybe weren't invented when the PRP radios were in service.  

Use the following information entirely at your own risk. If you can't accept that, don't use the information.  

Why did I bother with this project? 

I'm lucky to own a low-band VHF PRP radio that has the UK 4m VHF channels programmed into it.  These radios are not easy to find.  The VHF and UHF ones are more numerous. There was a time when there where bins full of them at radio rallies in the UK.

The PRP series are old radios and are generally obsolete.  As with all radios of this era they were supplied with old-tech NiCd battery packs.  If you are familiar with this technology the batteries have a service life and if you have a battery pack that is still working and holds a charge then your are very lucky.  Most don't even power up off the old battery.

So you have the radio that works, but a battery pack that doesn't.

You could re-cell an OEM pack with NiHM batteries, but your run into problems with charging it.  That is if you can get the battery pack open safely without completely wrecking it. Or you could try putting some Li-ion batteries into the original, but slight problem is that the readily obtainable 18650 ones don't fit inside.

The answer is to update the battery pack by replacing it with one that has Li-ion batteries.  Here two 18650 2600mAH are used, along with a 2 cell balancing board from eBay.  The original charger cannot be used, so instead a charging port is put on the battery pack itself, and a separate charger is used to charge the pack.  This modernises the radio and saves it from the landfill or just gathering dust in a box of junk. 

Note: if anyone from Philips / Simoco is reading this and judges that it is infringing some of your IP, just let me know and I'll take the information off the internet.

Battery Pack Connections

There are a couple of resistors needed inside the battery pack.  There isn't much information on these around, but after a search F5JTZ had some information on his website. Although this was for a battery eliminator, the values are needed for the battery pack.  There is also some useful information about the radio here as well.

The connections are made by using M3 C/S screws around 6mm long. The screws where helped into position by warming them with a soldering iron just so that the PLA softened. Instead of a nut to hold the screw I used one of the embedded nut fasteners with a slot cut carefully into it so that it could be tightened with a screwdriver.  The connections were made with wires attached to solder tags that were filed down so that they did not short circuit.  Once in place check the wiring does not show a short on your test meter and then put some non-conductive material in between each of the contacts. You could use glue gun if you like but some heat-shrink can be used, taking care not to overheat and melt the PLA case.

That's it for the instructions.  The rest you should see in the pictures on this page. I'm sure you could massively improve on the use of screws for the electrical contacts.

I don't offer the printed parts for sale as there would be limited demand.  If you want to give the project a go, drop me a line to

Parametric Box Spanner / Wrench

This one will be handy for the maker community.

When you are fitting a pot or an encoder you often need a 10mm or a 14mm spanner/wrench to tighten up the fixing nut.  On many occasions I've used pliers for this, and when I've slipped with the grip on the nut have put a nice scratch in the enclosure.  A printed box wrench makes this less likely, but you can scratch finished surfaces with almost any tool, so still use it carefully.

The design presented is parametric.  Fill in the spreadsheet with your dimensions, clearances and preferred wall thickness. The clearances for the nut in the spanner / wrench suit my printer. Yours may need tweaking. Print the first 10 layers or so of each end to gauge the print to save wasting filament while you get the clearances right.  You can also change the AF - Across Flats distances for any combination you like. I think the spreadsheet should take care of it. Otherwise just have a play to get it right.  The design was made in FreeCad 0.18 and the macro you download to convert the spreadsheet into dimensions is called EasyAlias. Google will guide you on how to use this in FeeCad.

In your slicer, arrange the larger hex socket to print closest to the bed, with the smaller one above. This will mean that you don't need support material.  A brim is recommended for a little more additional adhesion to the bed while printing.

If you want the STL file for 10 and 14 mm let me know via

Once again, I don't offer this as a printed part but if you would like one making up, drop me a line.