connecting 24 position rotary switch from CB radio AND what's this meter? - Page 1
Forum section: electronics / beginners

author: dentaku
author_rank: Frequent Contributor
timestamp: June 07, 2013, 03:36:23 pm
content: I found a very dead ancient 1975 Midland International CB radio at a campground this week an it has this big chunky 24 position rotary switch along with other interesting stuff like a volume knob with a clicky on off switch built into it etc. (I was 3 in 1975 so it's interesting to me). It's funny to see incandescent bulbs where LEDs would be these daysHere's the manual for it.http://www.cbtricks.com/radios/midland/13_882b/graphics/midland_13_882b_om.pdfand the schematicshttp://www.cbtricks.com/radios/midland/13_882b/graphics/midland_13_882b_om_sch.pdfQUESTIONS:Can anyone help me figure out the pinout, if you an call it that, of this 24 pin rotary switch (or is it NOT a standard rotary switch?). It's not like the simple 3 position rotary switch I found in this radio that has one input and 3 outputs.I'm not trying to fix anything, I just wanted to experiment with parts.It's a big old clunking 24 pin ALPSit says D C Japan94V-1A triangular logo with CCL 71FR VIt also has a little meter that according to the .PDF is the S/RF Power meter. "This gives the relative strength of incoming signals when receiving and RF power when transmitting"What exactly does this meter measure. I googled a bit and found that CBs have SWR meters.I'm guessing they're really not useful for anything other than radios/antennas?If you send audio to it and put it to your ear it works like a tiny speaker.

author: c4757p
author_rank: Super Contributor
timestamp: June 07, 2013, 03:49:26 pm
content: The meter is almost certainly a simple ammeter, and the radio drives it with a signal strength-controlled current. DC, not AC.

author: PA0PBZ
author_rank: Super Contributor
timestamp: June 07, 2013, 08:01:02 pm
content: You can see how the switch is working in the schematic, they clearly had no PLL back in those days so they used 2 handfulls of crystals to mix the right frequency. I doubt you can use the switch for anything else easily but who knows, be creative.The meter is a standard moving coil meter, probably 50 or 100 uA full scale, so depending on what you want to use it for you need a series resistor to make it work.

author: dentaku
author_rank: Frequent Contributor
timestamp: June 08, 2013, 12:40:21 am
content: Yup. After posting this I looked at the schematics (I edited the post to add the link later) and saw that it was probably more than just a regular switch.The switch had 12 little metal can crystals on clear plastic stands surrounding it labeled X1, X2 etc.When I checked it out with my meter I noticed that one pin can be connected to 3 other pins sometimes and it seems so randomI guess I'll just have to mess with it some more. It's just such a nice switch with two metal balls and two little leaf springs putting tension on them to give a nice definite click, plus the pins are perfectly spaced to fit in a breadboard or a floppy drive / IDE ribbon cable.Looking at it some more I think I can see a way to modify it to make it more useful since it's huge 1975 technology that you can actually work on.Thanks for the info on the meter too.Quote from: PA0PBZ on June 07, 2013, 08:01:02 pm

author: codeboy2k
author_rank: Super Contributor
timestamp: June 08, 2013, 03:45:17 am
content: wow... CB radioBrings back some memories... back in the day I had a Cobra 139XLR 40 channel single-sideband base station, a D104 mic, some big ass 1/2 wave vertical dipole in the air, and a home made 500W linear amp (yes it was not supposed to have that much power)I got out long before I had a desire to put up an antenna that was 2 times wider and 4 times taller than my house.Pics included for the benefit of those who grew up only knowing the internet(these are random pics I found on the net, not my setup)

author: dentaku
author_rank: Frequent Contributor
timestamp: June 08, 2013, 01:58:21 pm
content: The great thing about them these days is that old CBs have all kinds of interesting parts in them that can easily be unsoldered and used by absolute beginners like me just for fun.

author: Robby
author_rank: Newbie
timestamp: July 25, 2014, 02:18:54 am
content: My first post here on the EEVBlog/forum.Yes this is an old thread. But I had to comment on it since it is the only one of its kind that could be found in the search engine.CB radio is alive and well, thank you very much.Although I am a Ham operator, I have decided to use fixing old and new CB radios as a vehicle to learn electronics. In this endeavor I have been pretty successful, as I repair/unmodify/align local radios for Hams and CB radio operators alike that have these radios. In fact, it is a thriving hobby over the last few years due to decent RF propagation conditions. Still need to learn far more, as I am not satisfied until I feel comfortable fixing other things besides radios.Also, I needed an inexpensive DMM, so I chose the Uni-T UT-61E for electronic work only from what I've read on this forum and from mjlorton as well.I have seen more than a few Hammys post here on the forum. Surprised that there aren't more EE's that have gotten their license.Hope to tap into the brain trust here, and also to contribute some worthwhile posts.-Robby