My PCB Fabrication Process

Desulfator

My last desulfator design was Rev B. I decided it should be Rev A (even though Rev B is etched on the board), as it was the first desulfator board I actually built. For future reference I'm doing major revisions A, B, C, but minor (and or pre release) tweaks 001, 002, etc. So this should be Rev A 003, I think.

For more information on the desulfator see my previous post here.

Specs / Limitations

• When I do the layout I've found I can etch down to about 0.010"(50% success), but 0.020" is much more forgiving (80+% success). So I do most of my traces as 0.020". but they won't fit between some pins, so I run a 0.020" trace as close as I can, end it, put a 0.010-0.012 trace in the tight spot, end it, and continue with a 0.020 trace.
• I try to maintain 0.025" clearance around traces, since I don't use a solder mask it helps me avoid bridging traces.
• I flood-fill everything I can, the more copper I leave on the board the quicker it etches.
• So far I only do single-sided boards. Hasn't been a huge issue yet. I'd be tempted to just order 2 sided boards when I need them.

I use the toner transfer method for both the etch resist and the silkscreen. As far as prep it goes like this:

Copper Side First

1. Sand board with 400grit (wet sandpaper) wet with just a drop of dish soap
2. Dry board with a paper towel
3. Apply rubbing alcohol and dry with a paper towel.
4. Print resist on a piece of shiny paper, I have varing results with this, seems to depend on the paper I find. I read that the (glossy) whites of newspaper / magazine ads worked the best, but I find that some heavily colored ads have more of the wax / clay stuff on them and work better for me, with the exception of the silk screen side (more on that later)
5. Align board and paper, either fold the ends over to keep it in place or use a tiny piece of tape. Then run through laminator 5+ times.
6. Soak in cold water until paper starts to dissolve. Some times it peels off, other times I have to rub it until just the toner remains. sometimes I loose traces and stuff, if it's not too tight I continue, otherwise back to step 1.
7. Gently dry and examine carefully, touch up little holes in the flood fills and broken traces with a permanent sharpe(3 coats).

Etching
For etching I use cupric chloride, it works really good above 60F, somewhere around 40-50F and below it's really slow. It needs to work fairly fast, the majority of the problems I've had with it were when it's cold out and instead of 20-40 minutes it took 2-3 hours.

I keep it out in the garage, as I prefer not to risk spilling stuff like that in the house. (I don't want to spill it out there either, but I have better ventilation and access to a garden hose for emergency clean-up)

    8. Etch until traces are isolated.

    9. Rinse thoroughly, then Sand with 400 grit to remove toner, should look
        like this: (note the 2 is missing from the 2013? yep, didn't transfer perfect)

Bottom

Then the Front (silkscreen)
    10. Dry then drill two holes (for through-hole parts) as far apart as possible
          (either corner would be good) and use them to align your silk screen (do
          steps 3-6). I poke a wire right through the board and paper for alignment.
          (remove wire before running through laminator) Note: I try to use mostly
          white paper for this as the colors tend to stick.

Top

When it's all assembled and tested I spray the copper side with several thick coats of Rust-Oleum clear coat.

RobertShaw HS780 Teardown

I recently replaced a old furnace with a 90+ for my father, I don't recall the make or model of the old furnace, but I salvaged some parts from it to look at. Today we have a Robertshaw HS780 Hot Surface ignition control. The furnace was working, so there wasn't a failure to fix, but it may be of some interest.

RobertShaw HS780

If you watch the video be warned, It's my first attempt at an ad-lib teardown. I kept talking as I figured out the board and was a bit off. It's not bad, hope to do better next time. I think the left small relay is the gas valve, the right one powers up this board when the thermostat closes.

Top

Bottom

By far the most common failure on HSI ignition systems is the ignitor (not this control). They are fairly fragile. Never touch the heating part, it could cause early failure.

Diagnosis would go like this:

• 120VAC present at terminals labeled 120 and NEUT?
• 24VAC present at TH and TR? (thermostat calling for heat?)
• When calling for heat is 120V present at  IGN terminals AND HSI not glowing? (if yes replace HSI, if no suspect large relay)
• HSI Glows and 24VAC present between VALVE and GND? (if yes, suspect gas valve / safety switches/wiring, if no suspect outer small relay)
• Failing all that test the inner small relay, inspect all solder joints for failure and caps for leakage. (if you can't find anything at this point consider replacing the control.)

Sometimes a relay will actually fail (shorted coil, open coil, or bad contacts) and they can often be sourced for $5-10 from digikey or a similar company.

Video Notes:

1. The fan/limit control won't come apart easily.
2. Typical setting are ~100 fan off, ~120 fan on, ~180 high limit.
3. You shouldn't be bouncing off the high limit, if you are you have an airflow problem, oversized furnace, etc.
4. Flame sense is through the ignitor.

Lead Acid Battery Desulfator

UPDATE 2:
My parts have arrived, I've got the schematic sorted out (I think). I think I'm going to do a start to finish post on my current PCB fab procedure and make a new board, even though the other one seems to work. I've got the correct parts and the other pcb is together and working. I'd like to see if they work differently.

Desulfator-RevB - KiCAD 3D Render

The Theory:
When a lead acid battery sets discharged sulfate crystals form on the  plates, reducing the surface area and thus potential capacity of the battery. A desulfator pulses a high voltage / current spike into the battery that causes vibrations that knock the sulfate crystals off the plates.
The usual frequency is around 1khz, though the vibrations are usually in the mhz range. It's described as ringing a bell. The desulfator rings it a thousand times a second and the harmonic vibrations actually do all the work. Therefore the actual frequency doesn't seem to be particularly important.
It would probably be best to remove the battery from the vehicle so we don't pulse high voltage through computers, regulators, etc. It may take a week to several months to restore a battery anyway, so doing it out of vehicle is preferable anyway.

Desulfator Rev. B - Top

The Specs:

• Unit is controlled by the venerable 555 timer, although an attiny would work and allow more control / monitoring of progress.  (Possible future design)
• Should work on many voltages
• May work on nicad's too.
• This is basically a reference design. I want to see if (and how well) it works before spending a lot of time designing my own system (if I even need too, let's not go reinventing the wheel right?)
• I'm trying for a compact design, altoids tin or smaller. preferably 50mm x 50mm, as if it works well I may get a batch made and try to sell them.

Desulfator Rev B - Bottom

Limitations:

• As the battery size increases the amperage needs to increase. Two resistors can be replaced with pots to adjust the frequency and duty cycle of the 555, but this results in increased heat on the inductors. (we'll try the default settings to start)
• Increased amperage requires bigger, more expensive inductors.
• It's not self-powered, so a trickle charge is needed for operation.
• No reverse - polarity protection, hook it up backwards and you will probably destroy it. (I'm going to look into this, doesn't seem it would be too hard to prevent this, definitely looking into this before selling any)

Notes:
I'm basing this on Ron Ingraham's design, I don't think he followed the component numbering of the original, so if they say you can substitute something for R1, it may not be R1 in the schematic.

Update 1:
My parts haven't arrived and I've run out of patience. So I scrounged some inductors (about 600uh and 180uh) substituted some other parts and it seems to work.

Only found two problems:
1. I  missed a trace (somehow missed it in the schematic) and that prevented the duty cycle from dropping below 25% and caused the frequency to change with it. it was really frustrating. I eventually found it and added a bodge wire. Now RV2 adjusts frequency and RV4 adjusts duty cycle. I also added a 180K resistor to RV2, but that's just because I only had 100K pots (should have been at least 300K+. I highly recommend using pots for these. Then you can just dial it right in. (with a power supply and scope or by ear and watching that nothing gets hot)
2. Stupid (me) used non-polarised caps (C) instead of polarised caps (CP) in the schematic, so 3 caps were backwards.

I've corrected all these things in the schematic. I need to clean up the schematic and get it uploaded. I'm not sure if I'm going to roll all this into Rev B or go to Rev C. I have made a number of minor changes, but it's not a redesign by any means.

Rev. B Changes:
1. Replaced R2 & R4 with Pot's for adjustment. Resistors should fit instead, so it's optional
2. Added C41, C43 for more options on the low esr cap.
3. Noted in schematic different options for assembly.
4. Has component locations for several variations on the circuit. Board shouldn't be completely populated.
5. Might have placed the power connector on backwards. Oops.
6. PCB layout is Copyright for now. Free for Personal Use. I may release it to public domain eventually. I just don't want anyone selling these untested boards yet.

Links:
KiCAD + PDF Files

Make sure you add the cache library at the very top of the KiCAD libraries for the schematic. It's a PITA it doesn't do this automatically. The PDF's may or may not work, they gave me a fit. Make sure you print at 100%, no scaling.
Pictures of latest board in my PCB Fab post

Desulfator Information (mine is based on the low power - Ron Ingraham design)

My Failed Fan Controller Design

I've spent all the time and resources I'm willing to on this project for now. I may complete it at a later date. It all works except the input voltage from the furnace transformer is too high after rectification (38-40v).  The 78M05 I'm using is 35v max and it doesn't tolerate any more. It doesn't seem to damage it, as even after testing as bad on the furnace it works fine on 18v (max on my lab PS) I tried to build a SMPS replacement based on Roman Black's design, that also worked fine on 18v and blew at least a zener diode when on the furnace. I used parts I had on hand, so sometime I will get precise values and try again. For now I'm ordering a snap-disk. Perhaps some of this design may be useful to someone for other purposes. It really sucks, as the controller works fine, I just can't get the voltage regulated to 5v. If you have any ideas feel free to comment. It's probably easy and I'm just not seeing it :)

My Dad's woodstove is ducted into his furnace. It works OK, but he has to manually turn the blower fan on to circulate the air through the house. This is OK when they're up and keep the fire going, but if they don't get up during the night the fire burns down and it circulates cold basement air. Brrrr

I realize I could just use a therm-o-disk, but what fun is that?

Plus I get a bit more practice making boards. NOTE: I bumped the zone fill clearance from .020 to .025, that definitely helped me not bridge pins to ground. It's a simple board and I used mostly .025 traces with a few .012 and .080 ones as needed. I can etch .012 very consistently, even .008 fairly well, but I keep tearing pads off drilling. The extra copper seems to help considerably. Extra copper around pad make things much easier drilling and mounting. Essential for wire connections. My first board's traces got torn up where wires mounted (all .012 traces). Notice the pads across the top of the following image compared with the bottom of the board above:

 Requirements:

• Run off furnace power (28VAC)
• Switch fan on at approx 120F, off at 90f
• Make sure fan runs at least 10 minutes when turned on.
• Cheap, hopefully less than a $15 T-O-D

Specs:

• Controlled by a attiny85
• PCB was done for a full-bridge rectifier, but we may use a half-bridge to keep the voltage under control. (use 2 diodes instead of 4) (Note: Didn't Work)
• Used Salvaged Components where possible

Parts List:

• Attiny85 ($1.30) 
• lm335a Sensor ($1.00) (I had some of these, I would use a mcp9700-e/to($0.25) in the future. the board supports it, just omit the 2k resistor)
• lm7805 Regulator ($0.50)
• 2n7000 mosfet ($0.60)
• 2x 1n4007 diodes ($0.50x2)
• 330u 50v cap (salvage)
• 10u cap(salvage)
• 0.1u cap
• 10K resistor
• 2K Resistor (omit for mcp9700)
• RY5W-K Relay (salvage)(you can get ones with ~30ma coils for less than $2.50 and drop the mosfet, though a mosfet does make it more robust IMO) You could also try a solid state relay

Schematic

The 7805 was a bit close to the cap, that will be fixed in the linked files. I intended to use a to-92 regulator, but the one I had was rated for 100MA. I thought my relay was 150MA. It was a last minute change. As it turns out it uses about 9MA idle and 54MA with relay powered. I could have used the to-92 after all.Total cost was under $5, though to buy all the parts would be more like $10, the cheapest T-O-D I found was $8. If I have the wrong temp with this I just reflash the chip, with a T-O-D I buy a different one.

Code is in Arduino, you will need the attiny85 hardware files, a programmer or an arduino, some wires and bits. See this guide for more information. I may redo it in AVR C sometime, I just wanted it up and running. I didn't need to do anything special.

 /*  
  Fan Controller intended for a attiny85, but takes ~3k, change pins below for arduino and uncomment the serial for debugging on the arduino.  
  it's intended for a furnace, so no fancy pwm or anything, thought it wouldn't be hard to add.  
  Stephen Evans - stevesfixitshop.blogspot.com  
  */  
    
 #define INPIN 3  
 #define OUTPIN 2  
 #define ONTEMP 48  
 #define OFFTEMP 32  
 #define DEL 600000  
   
 unsigned long wait = 0;  
 int avread = 0;  
 int ain[10];  
 int i = 0;  
 void setup() {  
 // Serial.begin(9600);  
  pinMode(OUTPIN, OUTPUT);  
 }  
   
 void loop() {  
  //make 10 readings  
  while(i<=9){  
   ain[i] = analogRead(INPIN);  
   delay(10); // wait for adc to stabilise  
   i++;  
  }  
  i=0;  
    
  //average the readings  
  avread = 0;  
  while(i<=9){  
   avread = avread + ain[i];  
   i++;  
  }  
  i=0;  
  avread = avread / 10;  
    
  //Convert reading to degrees C  
  float sensorValue = ((avread*4.8)/10)-284.15;  
 // Serial.println(sensorValue);  
    
  // turn fan on  
  if(sensorValue >= ONTEMP){  
   digitalWrite(OUTPIN, HIGH);  
   wait = millis() + DEL;  
  }  
    
  // turn fan off if below set temp and delay has passed.  
  else if (sensorValue <= OFFTEMP && millis() >= wait){  
   digitalWrite(OUTPIN,LOW);  
  }  
  // every 50 days millis rolls over to 0, this makes sure it doesn't mess things up  
  else if (millis() <= (wait-DEL-50)){  
   wait = millis();  
  }  
    
 }  

Parallax 7345 SMPS Repair Tips

I started this as a reply in the Parallax 7345 RV Power Converter (SMPS) post. It quickly grew to the point I decided to tidy it up and make a new post out of it. Most of the specific info is for the Parallax unit though it may apply to other SMPS's.

Most of what I know about SMPS repair comes from reading: http://www.repairfaq.org/sam/smpsfaq.htm If you intend to work on a SMPS I strongly suggest reading and digesting the contents of it first.

Possible Problem Areas

Quick Disclaimer or "Safety Third":
Be very careful! There can be potentially lethal voltages all over the board even when disconnected. At least one heatsink is live! Proceed at your own risk!

Again, be careful, It's hard to diagnose a SMPS without powering it up. Usually a isolation transformer is used. I've toyed with the idea of using an inverter or generator for this. Basically you don't want the neutral tied to ground, you want it floating, then it's only dangerous between the line and neutral rather than line and ground (that you're standing on). All household / shore  power is referenced to ground at some point.  Depending on the wiring of your generator it may or may not be. I'm not sure how to advise you on this, no matter what you do there is a risk. Try to minimize it.

Check the obvious and make sure the problem lies inside the unit.
That said, I'd follow the power through the unit as much as possible. Start where the 120v line connects, I've spent hours searching boards for a problem only to find it wasn't powered to start with. make sure you have 120v going into the board from your generator / line connection before disassembling the unit.

After you can disconnect power, let it sit for a couple hours then disassemble it. Still be careful what you touch, use the one-handed method until you get the board out. turn it over and check the voltage across the two big caps, it should have bled off, but could be over 150VDC (I don't recall the voltage spec on them, assume it's fairly close to it). If they are zero (or at least below 20V) check the continuity from each power-in line to the bridge rectifier (just after the MOV, Square thing with a heatsink) it should read almost zero ohms (if it's several thousand your problem lies here).

Always look for obvious damage,burnt components, etc. 
Sometimes a burnt component is caused by a faulty but perfectly good looking component, so don't assume you found it, you may replace it only to have it go again. (A failed triac on a Maytag Neptune washing machine will destroy a resistor, replace the resistor and it will destroy it again, replace both and you can wash clothes)


That's as far as I got on this one the problem was rather obvious, so I'm out of specific information on it. As I noted it's basically a big smps, The document at the beginning of this post should help you with the basic operation. I marked some things on the above image, you may need to check how to actually test these, but hopefully it will give you a start. As always Google is you friend, just looking for more generic SMPS info than specific Parallax info should help.

These are worth checking, roughly ordered from most likely to least (imho):

1. Bad Capacitors, look for bulged , burst or leaking caps, they cause all kinds of headaches
2. Output resistors. You can see these have been really hot, but are working fine on this one. However if one failed I'll bet the rest would go within seconds or the output would drop dramatically. They should be a low ohm value(0-1R). 
3. Switcher Mosfet(s) - handles all the power, it should switch on and off really fast (100khz to several mhz, depending on design) this is connected to one of those big heatsinks, probably the live one.
4. Logic / Startup power. I might be off the mark with this, but I think without this resistor the unit will not start. It requires some power to get thinks going, I think it comes from here. Not sure of value, but shouldn't be open and probably fairly high(100K+?).
5. Bridge rectifier - if this goes you will get low(or no) voltage on the caps, unit may not start.
6. The logic section, the most complicated part of the system. Controls the whole thing, depending what's wrong it may be un-repairable (bad microcontroller, even with a new micro you won't have the firmware) or could be something replaceable (op-amp, pwm controller, etc.) I put this last because I know of one that survived 240V on the input, so I assume it's pretty rugged.

AVR Dragon Jumpers - ISP for Atmega 168/328/etc

I've been trying my hand at etching pcb's lately. As a result I needed to burn a bootloader on a Atmega 328 and I didn't put a ISP header on my target board. I really need to get in the habit of doing that. Usually I just stick it in my dragon, connect it up with a bunch of jumpers and burn it.

A while back I saw someone had made a whole set of boards for this purpose. You just plugged in the board and never get a wire crossed again! I made a brief search for them but couldn't find anything useful (schematic, pcb layouts, etc). So I made my own. So far I have made the ISP for the 168/328. Sometime I will make the HVPP for these and both for the 644/1284.

You may notice that I have a mix of male and female headers. When I got my dragon I put mostly female headers on (excluding JTAG and ISP) so I could use normal jumpers rather than special female ones. I still think it was a good idea, but most people use all male headers, so the board could use all females.

I only put the used headers for ease of use and cost control. For soldering I put all the headers in place on the dragon then added the board. It keeps everything perfectly aligned.

Etch-resist was a laser printer transfer, cupric chloride etch solution. I'll do a post on that whole process later.


I intended to attach the KiCAD Schematic and PCB file here, but I can't see how to do that (might not be possible), so I posted it over on TryThisTv.com