Friday, January 29, 2016

Double sided cold toner transfer experiment

I was very happy with the boards I made using the cold toner transfer method, and wanted to see how it would work for dong two sided boards. 

 I had a small board I waned to make that has a full ground plane on one side.  I printed the toner patterns directly in Eagle, making sure to mirror the top side.  The best paper I have found for this is Color Laser Gloss from Hammermill.  It is much thinner than photo paper but has the same glossy surface, and is only about $15.00 for 300 sheets.  

I cut the patterns in  long strips, and trimmed the top pattern so it had about a 1" overhang from the  each side of the toner pattern.  Then using a strong back-light I aligned the two patterns and taped the top pattern to the bottom.  I then stuck a piece of paper in between the two patterns to
protect the bottom pattern while I worked on the top.

Using an eye-dropper I placed a small amount of the solvent on one side of the prepared board blank., and slid it between the patterns. After positioning the blank I applied a few more drops of the solvent on top of the paper and spread it around until I could clearly see the toner pattern through the paper.


When It was positioned where I wanted it I placed a piece of printer paper on top and covered with a piece of blank circuit board.  I applied pressure for about a minute to set the toner in position.  I then removed the blank board and first with the paper still in place I used the back of a fork to burnish the toner pattern.  After a little while the paper began to become more opaque.  Then I removed the piece of printer paper and continued the burnishing with medium pressure.  

 When it looked like all the solvent had evaporated from the paper, I turned it over , removed the piece of paper that had been there to protect the bottom toner pattern.  Carefully lifting the pattern slightly I put a few drops of solvent on the board blank and spread it around until even.  I added a little more solvent to the top of the paper until I could clearly see the pattern.  I processed this side the same way as I had the other.

 I checked the board and everything looked fine.  I found one or two small pinholes in the toner on the large ground plane area that I touched up with a marker.  After etching I drilled a couple of holes in the board to check registration.  The photo shows the same hole as seen from both sides of the board.  The registration was much better than I had ever been able to get using the hot method with a laminator.

Sunday, January 10, 2016

N6QW Simple-Ceiver Audio Amplifier testing

I finished building the audio amplifier stages of the Simple-Ceiver and with a speaker hooked up I got a response when I touched the amplifier input.  That is always a good sign, but I wanted to check to see how quiet the amplifier is and the frequency response of the amplifier.
For checking audio stages my favorite program is Visual Analyzer available at

New-Mini-USB-2-0-3D-Virtual-12Mbps-External-7-1-Channel-Audio-Sound-Card-AdapterThis is a PC based software that uses a sound card as the instrument. Not wanting to blow up the sound card in my PC if I do something stupid I use a really cheap USB sound card I got on eBay. This also has the advantage that I can connect it to the computer near my work bench with a USB extender cable, and only have the small unit on the work bench.  I have also used the same card to build a digital mode interface.  The one I usually use is this model and is available for less than $2.00 with shipping.

Visual Analyzer software is a utility package of audio related functions.  It has an oscilloscope, AF Spectrum Analyzer, Signal Generator, Voltmeter, and several other functions I have not used.
With a little additional circuitry it can also be used as a ZRLC meter.

I connected the output of the sound card through a 2.2uF capacitor to the top of the 10 K volume control and the input across a load resistor instead of a speaker.
Setting the sound card to output a 1 kHz sine wave, I adjusted the  output level and gain pot to the point just below where I saw any clipping on the signal.  Then I changed the signal to Pink noise and set the spectrum analyzer to average 100 traces.  This makes a nice clean display of the frequency response of the amplifier.  As shown in the response curve, it is fairly linear to about 12kHz. and then falls off sharply to its low level at around 14.5kHz.
Still waiting for a couple of parts to arrive.  One of them is the 100mH inductor in the output filter of the product detector.  After these arrive I will do a plot of the complete Audio section.


Cold Toner Transfer Circuit Baords

For years I have been using the toner transfer method for making circuit boards.  I have an old Brother printer and a Scotch TL902 laminator that have worked well for this.  One of the problems I have found with this method is that the type of toner you use is very important.  If I use real Brother toner, I get very good results for most of my boards. I have tried using generic toner cartridges that are about 1/3 the price, but have not been able to get very good results.  Another problem is with large ground plane areas, I have  had problems with etch through, and pin-holes showing up in these areas.

I recently saw a post on Instructables about using a chemical method instead of heat to transfer the toner to the circuit board material.

Since my Brother toner cartridge was just about out and I would have to order a new one fairly soon, I decided to give it a try.
Looking around all my painting supplies, for solvents I found a can of denatured alcohol. The original article used Acetone , which I did not have, but I had  some Xylene I had used for thinning and cleaning up some enamel I had painted.  

I printed up several copies of a board I need to etch using the generic toner cartridge.  Playing around with different mixtures of denatured alcohol and Xylene.  I found that a 5 to one 1 mix of alcohol to Xylene would soften the toner without causing it to smear instantly.  I tried the method as shown in the video with fairly good success, and then tried to modify the method a little.  Here is what I came up with.

With an eye-dropper I put enough of the mixture on a cleaned board to evenly cover the board.  Then place the printed paper on the board and moved it around to position it properly on the board. 
After it was positioned on the board, I used the eye-dropper to saturate the paper with more of the mixture.  You could see the paper becoming more transparent and clearly see the toner pattern.
I let this set for about 30 seconds, and then covered with a folded over paper towel.  I then placed another piece of circuit board material on top of the paper towel and applied pressure for about 2 minutes.  After that time I removed the top board, and used the rounded back of a fork to burnish, through the paper towel.  After  it looked like much of the mixture had dried, I removed the paper towel and burnished the laser paper directly.  You could clearly see the toner pattern through the paper.  After a couple of minutes of that, I left everything set for a couple of minutes for the last of the mixture to dry.
After it was dry, I soaked the board in water for a couple of minutes, and removed the paper by lightly rubbing with my fingers.
The toner on the board looked nice and crisp, good adhesion all over, and no sign of smearing.  After etching the board, I found very nice traces, no problems where traces went between IC pins.
Also found nice smooth ground plane areas, with no etch through, or pin-holes.
Looks like I will be able to save a lot of money on toner, and finally retire the laminator.  Probably only used about a half a teaspoon of the mixture, so the remainder of the quart  cans of alcohol and Xylene I had around should last a very long time.

Just a couple of pictures of the boards done with this method.
The completed board, and a close up showing the sharpness of the etching , and nice solid ground plane area without pin-holes.

Now to get to doing something with these boards.