After linking my two posts on the Cold Toner Transfer method to
https://groups.yahoo.com/neo/groups/Homebrew_PCBs
there has been much discussion about the danger of the chemicals involved.
Some of these mentioned the effects of day to day heavy exposure found in some industries. The amount of chemicals used in this method is minute in comparison. I still have about a third of the 4oz. bottle of mixture I made up after doing 3 single sided and and 3 double sided boards.
But .it is always advisable to take precautions when working with any chemical. Even the most common such as dihydrogen monoxide can be dangerous under the right condition.
Years ago I made a simple air filter that I use when etching boards and soldering. It is very small and can be easily setup next to where-ever I am working.
I had a broken 12 v brushless fan from an old computer. I cut out the bottom of a disposable food storage container and glued the fan to the bottom, making sure the fan would draw air in through the container. I then glued a 9 v battery holder to the side of the fan and wired up a switch.
To the back of the fan I attached two of layers of zeolite air filter material, with a single ply of a two ply paper towel between them. The filter is just held on by twisted wires through the normal mounting holes in the fan.
Very simple and very low cost. Only thing I had to buy was the air filter material about $2.00 ( replacement air filter from a kitty litter box).
I can move it around between the soldering station, etching tank and board prep.
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.
http://www.instructables.com/id/Heatless-cold-Toner-Transfer-for-PCB-Making/?ALLSTEPS
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.
I spent most of the holidays visiting relatives. and had quite a bit of time to work on something I had been thinking about doing for a while. I have been following the development of the Simple-Ceiver that Pete N6QW has been posting on his blog. N6QW.blogspot.com .
Pete spends a lot of time going through the design of a DC receiver that is later converted to a single conversion heterodyne receiver for 40 meters. He goes through the design using LTSpice to simulate each stage before he builds them. This powerful tool allowed him to optimize the circuit design before melting any solder.
I have a bunch of 12 mHz. crystals left over from the IF amplifier for the Specan, so I could use the same frequency scheme that Pete used. I plan on using a version of the SI5351 VFO I had built for the "Canned Frog" transceiver. Different from Pete's circuit I will use another clock output from the SI5351 for the BFO.
Link to schematic at https://www.dropbox.com/s/dersy23jgj6h37c/Simple-ceiver-schematic.pdf?dl=0
After drawing the schematic and getting it checked by Pete, I did a single sided board layout using mostly surface mount components. I did not have surface mount versions of the ICs for the AF amplifier so I did the layout with extended solder pads for the leaded components. Although I plan on using the SI5351 for the BFO, I decided to add the BFO oscillator to the board.
Etched the board now to start building and testing the receiver, first the audio amplifier stages.
It is getting close to Christmas, and I need to come up with another present for my son. He always says that when he was a little kid he had wanted a game system, instead he got a real computer. He had been a programmer for a while so I guess it wasn't a complete waste. I think it is time to finally get him a computer game. Looking around I found a couple versions of the original computer 'PONG" game for the Arduino.
I chose the project from http://michaelteeuw.nl/
that looked like it would be easy to port over to the hardware I have on hand. And of course it would fit in an Altoids tin.
I had an OLED like the display in my "Canned Frog", but it was two color instead of monochrome. I had a small TFT display left over from the DL Watt meter project, so decided to use that.
Looking a the schematic, it was very easy to take the board layout from that project and modify it for use for the PONG project. I was able to remove the Dummy Load and detector components from the board, and move the Arduino Pro Mini and display up towards one end of the board to give room for the two pots I needed for the game controls. Only other thing was to bring out a pin to connect a small speaker.
After etching the board and installing the components, I started on porting the software to work with the TFT display. The main advantage of the software I chose, was that it had used the Adafruit graphics library. I had a compatible library for the TFT display I was using, so it was only took an hour or so to make the necessary changes to use this display.
Main changes was in the resolution of the display, and handling the different colors available to this display. The OLED display has a clear() function that was used during the draw routine that was not available in the TFT library. I tried to replace this with a fillScreen(color) function. Unfortunately this was much too slow and there was a lot of jiter. Instead of filling the whole screen, I used the fillRectangle(color) function to only clear areas that needed to be redrawn. This was much faster, and greatly reduced the amount of jitter. Just a couple of other changes of game play and the porting was finished.
The part of the project that took the longest was cutting and aligning the holes in the Altoids tin.
While waiting for some parts for the Spectrum Analyzer, I was looking around for a quick project.
There was a post on the QRP-tech yahoo group about the NorCal S9 Signal generator
http://norcalqrp.org/files/NorCal_S9_Assy_V1.pdf
This is very close to the circuit for the Elecraft XG2 Receiver Test Oscillator
http://www.elecraft.com/manual/E740084%20XG2%20Manual%20Rev%20F.pdf
This looked like something that might be useful for testing the Spectrum Analyzer after I get it finished. I decided to build a similar unit, using parts from both design. Looking at the NorCal circuit, I saw that they used 20 and 14 db pads instead of the single 34 db pad used in the Elecraft model. I went with the NorCal circuit and added switching around both pads to have options of 50, 10, 5, and 1 uv. outputs.
I want to put the signal generator in an Altoids tin, so I used the same template as my AD8307 power meter as the basis for the board layout. I have found that I get more consistent etching of the ground pour if I do it as a hatch instead of solid. I plan on using 2 row .1" header strips with jumpers instead of switches, so I placed extended solder pads on the board. This way I can just bend the bottom part of the header pins out to the side and solder directly to the top of the board.
Now to etch the board after I get back from a hamfest tomorrow.
11/8/15
Well it was a little damp and chilly at the Hamfest, so I didn't stick around as long as I usually would. This gave me plenty of time to etch the circuit board. For SMD boards I have been using the blue press-n-peel transfer paper to eliminate etch through, and I get a cleaner pad for the SMD components. I also let the boards sit in some "Liquid Tin" solution for about a minute to give a nice tin coating to the traces. This seems to solder a little better than the bare copper.
I built the oscillator portion of the board to test how much output I was getting. From the Elecraft document it looks like the oscillator should put out about -50 dBm before the attenuators. Hooked mine to my home-brew AD8307 power meter and got a reading of -48dBm. Checked the voltage to the oscillator and had about 1.6 volts, I might try adding another diode in series to drop the voltage and see what that does to the output.
Now on to the attenuators, I am missing a one of the values for the 20 db pad but will try with the closest value I have for now. Will replace with correct value when the assortment of low value SMD resistors I have comes in.
Since it is raining out I decided to finish the board and add the attenuator components. With the attenuator pads out I measured -68.2 dBm on my power meter. I added another diode in series with the existing diode, this dropped the voltage to the oscillator to 1.07 volts. Measuring the output with the additional diode I measured a value of -72.8 dBm. This is more than close enough to the desired -73dBm output level of the Norcal S9 generator.
Only have two crystals in the circuit for now (3.561 and 7.030) will add others as needed. Listening to the output on a receiver. The 50uv gives about a S7 reading, readings for other levels are below S1 but I can hear definite changes in the signal as I change attenuator settings.
Unfortunately I do not have any calibrated test equipment to verify the values I found. But I believe the accuracy should be enough for testing the home-brew equipment I am working on.
Link to dropbox for Eagle files and toner transfer image.
https://www.dropbox.com/sh/p4qqfqab0z5g80k/AACJtjIMUgUTV1FqEuiN-Byta?dl=0
I finished drilling some holes in an Altoids tin and and mounted the circuit board. I also printed a simple instruction card showing the jumper settings for the different signal frequencies and attenuator settings. I sized this to fit inside the top cover of the Altoids tin.
