All posts by Jeff

Electrical engineer, tinkerer, maker.
Microcontrollers

I programmed the RSTDISBL fuse.

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AVR microcontrollers use “fuse bits” to set various operational parameters of the device, such as the speed of the internal oscillator or the watchdog timer settings.

Most fuse bits can be set or reset without worry, that is, they can be flashed into one state and then flashed back again using an SPI programmer like the USBTinyISP.

However, some fuse bits are irreversable or at least awkward to change, similar to the code protection bits on a PIC microcontroller.

One example is the RSTDISBL fuse.  This fuse allows bit 6 of PORTC to be used as a general purpose I/O pin instead of the RESET pin.  Well, it turns out that SPI programmers need the RESET pin to flash the device.  (RESET is set as part of the routine to enter serial programming mode.)  Once the RSTDISBL fuse is set, no more SPI flashing is possible.  The only way to recover is with a high voltage programmer like the STK500, which I don’t have.

Too bad I didn’t realize that beforehand.

At least I’m not the only person who has done this before: http://support.atmel.no/bin/customer?=&action=viewKbEntry&id=13

Update: It’s alive!!!  I made a high voltage parallel programmer out of an Arduino, flashed the fuses back again, and the AVR came back to life.  The parallel programming protocol is well documented in the datasheet for the part and pretty straightforward.  I think I’ll transfer the circuit onto a perfboard just in case I ever need to do this again!

Electronics

Coil in a can

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Coil in a can

Last weekend at the Electronics Flea Market I picked up some very strange items, including this one, pictured above.  It’s a tin can that looks very similar to an ordinary soup can, except that it has the following markings on it:

R16-C-28604-15
COIL
QTY.1

NSC.OAKLAND JULY 1953
PRES METH. 2D

Thus far the only information I have learned from the markings are that NSC.OAKLAND stands for the former Oakland Naval Supply Center, closed a decade ago in 1998.  According to Wikipedia, NSC supplied components to the fleet in the Pacific during WWII.  Beyond this I have not been able to find any information.  Presumably this is a replacement part for some piece of obsolete military hardware.  A “coil” is another name for an inductor, a clue that this may be part of a radio system or other high frequency equipment.

After staring at this mysterious object for almost forever (a week) I decided to open it.  Realizing that the can could be full of cold war era hazardous chemicals, munitions, objects under high compression, or nasty sharp edges, I did this very carefully and documented the entire process of discovering the contents.

First, the obvious – opening the can.  Pretty straightforward.

Coil in a can

What’s inside?

Coil in a can

Weird.  Lots of oiled green paper.  Whatever is inside is packed very well, when the can is shaken nothing moves around.

This is the clump of stuff to come out.

Coil in a can

Packing material?  The precursor to styrofoam peanuts?

Below the packing material…

Coil in a can

What’s this?  Vintage dessicant!!!

The last object left in the can looks interesting.  It’s wrapped in oiled green paper and sealed with tape.

Coil in a can

Inside the paper we find this:

Coil in a can

Not a huge surprise – it’s a coil (inductor).  It has a knob or grabby thing on the top and a funny connector on the bottom.  It looks brand new.

Here are a few more pictures.

Coil in a can Coil in a can Coil in a can Coil in a can

The markings are “ARC” and “7270 239 KC”.  ARC might be American Radio Corporation?  239 might be 239 kHz (kilocycles)?  Hard to say, google didn’t turn up anythign interesting.

An impressive amount of stuff was packed into that can!

Coil in a can

This solves the mystery of what’s in the can, but what is it for?  Does anyone know?  I’d love to find out – leave a comment or contact me directly.

Electronics, Events

Electronics Flea Market @ DeAnza College

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Air variable caps.

Kylie and I decided to check out the Electronics Flea Market at DeAnza College this past weekend.  I took a bunch of pictures and put them up on flickr.

We met a trio of Evil Mad Scientists there and had a great time.  I stocked up on tweezers and tiny solder braid, along with some mystery items I’ll feature in an upcoming post.

The last Electronics Flea Market of the year is next month, on Saturday October 11th. Don’t miss it!

By the way, the big news this weekend was that HSC electronics is NOT moving as was rumored earlier in the year.  Speaking of HSC, this coming weekend is the annual HSC sidewalk sale.  (This year they’re calling it a warehouse clearance sale due to downsizing at their present location.)