drtwist's blog

you know you're hardcore when...

drtwist — Sun, 28 Dec 2008 23:35:29 -0600

you buy a personalized birthday song for your multimeter. Found while looking for a service manual.

Yes Virginia, there really is a group order this week

drtwist — Sun, 28 Dec 2008 11:16:17 -0600

UPDATE: due to the new years holiday, I've gone back to the monday deadline at 5 PM to accommodate the fact that UPS does not move ground shipments on Wednesday.

Apparently I can't post to the blabber list right now, so this post is the best way i can think of to get the word out that there is a group order for this week.

sorry for the late notice.

order goes out on Monday at 5 PM to Digikey and Mouser

relevant details, as always are Here

since I and others seem to be having trouble with the lists please email me directly at drtwist@aracnet.com and I'll try to have the current order page: http://spreadsheets.google.com/pub?key=ptkc9PHWxERzxMKpTtzLGMQ updated as stuff comes in

XR2206 Function Generator

drtwist — Sun, 21 Sep 2008 00:25:52 -0500

While in Norvac The other day I was browsing in the IC section and came across this little gem: I think it was the Jim-Pak packaging that did it (Jim-Pak was a single serving component vendor that has sadly gone the way of the sort of places that sold it)  The Data Sheet on it is here it's a pretty cool little chip that require very few external components to produce a square, triangle or sine wave. I mostly bought it because of nostalgia for the stores filled with Jim-Pak stuff of my youth (most notably Zero Gee. It turned out to be the best $2.40 I've spent all week.

It produces nice output too:

Laminators, Green TRF, and You

drtwist — Thu, 11 Sep 2008 23:35:24 -0500

I've always made PCB's by the Photo fab method, with varying but never entirely satisfactory results. I was also somewhat put off by the need to buy pre-sensitized boards, at ridiculous prices. at a meeting earlier this year I was talking to Don ( feurig ) about it and he suggested I try the Toner Transfer Method (note reverent capitals).  I'm completely hooked on the toner method. There are a ton of tutorials on using glossy ink-jet photo paper to do it, but don't bother get the good stuff from pulsar (digikey part number 182-1021-ND0 ). using the photo paper is a pain. you have to soak and scrub and mess around instead of just getting the paper wet and pulling it off.

But the Secret Sauce is Digikey part number 182-1021-ND also known as Green TRF.

The difference between Green TRF and no TRF is pretty obvious:

On the board on the left is the Toner Transfer Paper alone, and on the right I also used the Green TRF.

The other thing than makes toner transfer a treat is using a laminator. I use a GBC HeatSeal H110 (for no particular reason other than it was on sale at Office Depot that day.)

The big trick to using the laminator with TRF is to put he laminator on the "cool" setting,after warming it up a bit, not all the way on the "hot" setting, to get the wrinkles out of it before you do it with the laminator fully heated. if you don't do this the TRF smudges a bit.

Using the laminator with the Toner Transfer Paper is cake, just heat the laminator up and pass the board through a few times

DS1307 RTC Breakout Board Rev 1

drtwist — Mon, 14 Jul 2008 15:44:50 -0500

As part of my clock project (yet to be documented) I needed an accurate real time clock (RTC). I selected the Maxim(Dallas) DS1307. I based the decision mostly on it's popularity and because of the availability of C libraries for the AVR. Sparkfun has breakout board that's similar to this but i didn't feel like paying $20 plus shipping for such a simple board (plus I think that Don's parsimony is rubbing off on me a little). In addition I wanted integrated pull-up resistors in the i2c lines.

Bill of materials:

Digikey part#, item, price, quantity
300-8735-1-ND, 32.768 kHz crystal, $0.84, 1
DS1307Z+-ND,  DS1307 RTC, $3.29, 1
BH32T-C-ND, CR2032 battery holder, $1.04, 1
P189-ND, CR2032 battery, $0.28, 1
478-1831-ND, 0.1 uF tantalum cap, $0.46, 1
2.0QBK-ND, 2k ohm carbon film resistor, $0.27, 3 (these are what I used, you can substitute
whatever 1.8k-20k axial resistors you have laying around)
A36390-ND, 5 pin male header, $0.91, 1 (I just used some make headers I had laying around, 
I just found the equivalent on digikey for completeness sake. digikey/mouser/newark all have
terrible prices on pin headers)

total= $7.57

board supplies:
single/dual sided copper PCB
Toner transfer paper (digikey#     182-1003-ND)
green toner reactive foil (TRF)(digikey# 182-1021-ND)
Ferric Chloride etchant

parts placement:

top side after assembly:

bottom side after assembly:

PDF of etching pattern for the board is attached to this post. the libraries for this part for C and Arduino are all over. just google.

If I feel like it, I'll make another one that has jumpers on the battery and pull up lines, so you can clear the memory or turn off the pull ups if you want to. I'll probably rotate the battery to make the board smaller too. right angled header pins are another feature to incorporate, but i didn't have any on Sunday when i built it

for prototype purposes this will work just fine for now.

First prototype of my 6v6 amp is done!

drtwist — Fri, 04 Apr 2008 14:46:17 -0500

I finally have my 6sn7/6v6 based prototype done! I chased down a couple of noise sources and now it plays sweet, sweet music. Now I just have to put in a more permanent container and add a couple more features.

the amp itself is based on the venerable 6sn7 driving a pair of 6v6's in single ended configuration, with power supplied by a Hammond 270HX transformer and rectified and filtered by a 5y3 rectifier tube and a hammond 159Q choke. the output transformers are Trancendar tt-012-ot 's