Case nibbling revisited --- More AVR fun

George Heron sent me a private e-mail today that I think is worth mentioning.  I don't think, in my case, it would have made a difference because of the big variety of 1/8" stereo connectors I use.   I still think opening the slot up in the back of the case was the appropriate thing to do for me and the future diverse uses of the SDR-Cube.

HOWEVER, you might want to try George's suggestion first.  That is moving the I/O card PCB farther back in the case by sliding it back as far as it goes (I did that actually and it wasn't enough) and possibly by elongating the four mounting holes (I didn't try that) on the subchassis to make it go farther back into the case.  If you get the metal rims of the phono jacks a little past the outside of the case, then the connectors will not interfere.  But you will no longer have the +12V coaxial power jack flush with the case either.

I think, personally, I like the connectors slightly recessed which means nibbling the case.  But the other option is valid if you have issues once you assemble the cube.

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I had a "snow day" today.. we got about 4 in of snow out here in the great white North of Eastern Iowa.. I drive a front wheel drive car (my 4WD 1998 Explorer has a coolant problem and I've stalled for about a year on deciding to get it fixed or not.  I really want a full size 4WD pickup, used, to replace it.. and putting in $2K into a vehicle worth 2K?!?  I dunno...).  Anyway, had that thing still be running I would have had no issues.. but it was just bad enough today with the VW TDI that I thought "Vacation Day."

I did a couple of hours worth of work on the AVR board.  I decided that to band switch the amplifier I would use a 74HC138 3-8 demux (I acutally used an LS part).. then I discovered for the positive drive I needed for the 2N3904 transistor switches for the +12V coil relays.. that the '138 had the wrong output logic polarity (active Low)... So I figured, OK, I wanted LED's for a band indicator anyway.. I added a 74HC04 (actually another LS since I had it in the junk box) to the design.  I'm doing point-to-point wiring on that protoboard with scrap Teflon wire.  It makes you appreciate the invention of printed circuit boards.

Anyway.. I did get the whole thing working while taking only 3 of the lines from Port C (after 30 minutes of fiddling I remembered to set the fuse to disable JTAG on the part so there WAS a PORTC!) of the ATMega644.. since we only want one band selected at a time.. that is a hardware way of doing it.  Also if 12V gets to the logic it'll blow a 74LS04, a thirty cent part rather than the $8 AVR.

The board that is (temporarily) under the LCD is the LED band indicator (six LEDs).  Blue, of course!  :O)

The missing ground wire on the connector mounted to the LED board will go on a second connector for a couple of pushbutton switches.  I've not quite decided on how many.. 2 or 3.. I need to think through the GUI for this.

Only attempt this sort of point-to-point wiring if you can get a hold of Teflon wire.  PVC would have been a smelly melted mess:

Now I don't have room on the protoboard for the MAX232 driver for a serial port.. I'll have to figure that one out in a few days when I get to work on it again.  This is part of the reason I really like SMT on finished circuits (not protos like this one).. there isn't that much circuitry there for the size of the components which are quite literally huge for what they do.

'Till next time... it may be awhile since I'll need to make up some time at work now.  No snow in the forecast for the rest of the week, but highs in the single digits Fahrenheit.  I don't think human beings are meant to live at this Latitude...