28 October 2020

ICOM BP-84 battery pack

At a slow but steady pace I am working on a 10 GHz WBFM  receive chain not based on RTLSDR. The path requires having a receiver capable of WBFM at 600-700 MHz, which is covered by most "scanners".

Recently I bought an ICOM IC-R1 without battery packs, so I sourced one large enough to contain an energy source both for the receiver and the LNB.

I bet on a BP-84 hoping it would be tall enough to contain 18650 LiXx cell and it does indeed.

LtoR: BP-84 shell, AA for reference, 6x custom NiCd cells, 2x 18650.

Since the project around the IC-R1 scanner has been put aside in favour of another scanner, I will write only about "how to remove the original content of BP-84?"

First of all, the bottom cover must be removed. My BP-84 came with the cover already off: saw it off carefully since you will not split in two parts the shell. Once the bottom of the cells is exposed you need to cut off three metallic tabs (visible in the picture) which also hold in place the 6 NiCd cells. Once the three tabs are loose, the 6-cells pack can be pulled out with slight force.

A 18650 Li-xx battery is perhaps 1 mm taller than those custom size NiCd's. But given that the BP-84 bottom is now lost, you can handle the extra length when building a new bottom.

Three 18650 in [v^v] shape (zig-zag) should fit in there. That gives 12.6V to 10.5V. Consider adding a fuse and a Li-xx protection circuit. The 12V line can go out to a power injector towards the LNB so everything is self-powered. Enjoy!

13 October 2020

Kit Oscilloscope Clock 8SJ31J review - 3

Since I have written a review of this kit I have been asked to share pictures of my build. I am unsure how useful they can be, maybe just reassuring.

IMPORTANT. DO NOT RELY on these pictures to decide which component goes where. In order to build that kit you need to be able to use an ohmmeter to sort resistors, read IC markings and understand capacitor values. Also, the kit seller (that is NOT me) may change components depending on his sources, and some values too.

Click on pictures to get the larger version.

Direct all your questions and problem to the seller, not me.

All pictures are watermarked and cannot be used elsewhere.

How I stacked the two boards, size is about 20x8x7 cm.





11 October 2020

Kit Oscilloscope Clock 8SJ31J review - 2

After few days fiddling with the kit I came up with one further tip for future builders: use a "sort-of" socket for the two fuses F1 and F2. They are not resettable, so if they blow up you need to go back to the soldering station.

Obviously it happened to F2 (filament) in my built kit. Now I fit two machined pins and the new fuse will go there. Moreover I noticed that F2, whose value should be 1A, was marked 750 mA, barely the limit for 2BP1 CRT that requires 600 mA according to the datasheet (but probably more at power up on cold filament).

10 October 2020

Kit Oscilloscope Clock 8SJ31J review - 1

Since I got few small CRT tubes without driving circuitry, I took some time to think of a good way to test them and build a display of some information. I studied circuits found online, considered building just an HV power supply and reviewed DIY kits.

The kit way sounded good, but pricey. Nevertheless, since most firmware has been written and shared, I would have spent lot of time in reinventing the wheel without breathing life to the CRT. The kit choice leaves me time to plan a nice enclosure, instead.

In the end I picked a kit from China, available on aliexpress and other sources for about 60€ delivered. It had good reviews and the design is open (I have not checked if it is derived/copied from others). The original item name is "Kit Oscilloscope Clock 8SJ31J Driver Board Oscilloscope Clock Control Board Kit Creative". The documentation says it works with a dozen CRT models, but voltages are compatible with even more tubes, like those that I have.

The kit has two boards and comes in a packaging that is safer than most other shippings from China. Instructions must be requested by mail to the seller, but what you get is schematic diagrams, one BOM per board, troubleshooting+setup tips and CRT wiring for supported models.

At this point the feeling is like building a kit you have prepared yourself with few added complications: you don't know parts placement, you need to sort-out components (easy, use a DVM!), you have no mid-build smoke tests, some values will be different or parts missing.

Regarding different values (for resistors) you can understand the reason if you can read the schematic. For empty slots on the boards you can make sense of them by looking and studying the schematic diagrams as well. In 3 missing resistor slots I fit 5 Mohm ones to give a better look. I couldn't help, my eye kept falling in that area! (Those 3 resistors are pull-up for data lines which are - in my kit - already soldered in the rotary encoder board.)

Sometimes I found hard to associate the component place with its name because the board is quite dense. In some cases the part name (R54, C11... for example) could have been moved inside the symbol and provided a paper copy of the placement for future reference. Also some pads go directly to the large ground plane and with a small pad area they are hard to solder.

Very first power-up test.

If you will build this kit use your smallest iron tip and your largest patience: there are over 400 pads on the XYZ board and over 300 in the control board!