Hacked Toaster Oven for SMT soldering 

I usually hand solder SMT devices in the prototypes I make for clients. Some parts have a large pad on the bottom that needs to get soldered to a plane for heat dissipation or RF grounding. When I can, I put a large hole in the center of the pad so that I can solder it from the bottom after the other leads are soldered down. But, sometimes the part is too small for that.

I picked up a cheap toaster oven to do reflow soldering as described in many places on the web. It worked marginally well. There were two problems. 1) The highest temp setting was right at the solder melt temperature threshold, and 2) the temperature swings were awful since it is a simple bi-metallic strip thermostat.

A while back, I picked up a pair of Omega CN7000 temperature controllers at the Valley of the Moon Amateur Radio Club hamfest in Sonoma. One had a bad display, and the other was missing the output relay. I swapped parts and ended up with one good controller. Time to start hacking...

Here I have taken the end cover off the toaster. You can see the thermostat and control switches at the top left, and the timer with bell at the bottom. After figuring out how it was connected, I removed all of the controls in preparation for adding my own.

The toaster needs about 11 or 12 amps with all of the elements turned on, and the relay in the CN7000 is only rated at 9 amps. Luckily I had a 20 Amp rated relay with a 110VDC coil in my junk box. I mounted this to the inside of the end cover and started wiring it all together.

The toaster has two pairs of elements, one on top, and one on bottom. Each pair is connected in series at the far end, and the pairs are connected in parallel at this end. The center wires of the elements get really hot, so the original used welded connections. I left some of the original wire intact on each element, bent it into a small circle, and used SS screws to bolt the connections together.

The main power cord comes in and the hot side goes to one of the contacts on the relay. The neutral goes to the big wire nut, and the ground wire goes to the chassis of the toaster. One side of the series/parallel heaters goes to neutral, and the other to the other side of the relay. Two bits of zip cord go out to the CN7000. One provides power to it, and the other goes to the output contacts to switch power to the big relay coil.

The diode next to the relay coil converts the 110AC to 110DC. This picture doesn't show the 10uF, 200V capacitor also required. I know, running 110AC through a diode doesn't give you 110DC. But, it's close enough to operate the relay coil very nicely. In fact, I could use a smaller capacitor since short "off" times from the controller don't open the main relay.

I buttoned it all up and gave it a spin. My procedure is to set the controller for 150C and let the oven warm up while I prep the board. I put solder paste on the pads to be soldered (using a toothpick), and put the parts in place. The paste does a decent job of holding them while I move the board to the oven and put it on the rack.

Close the door and wait about 3 minutes to bring everything up to temperature. Then, I set the controller for about 210C and watch the temperature climb. When it gets to about 195 and the solder starts to melt, I wait 30 more seconds and then pull the plug. Wait another 30 seconds, and then open the door to let it cool. After a couple of minutes I pull it out of the oven completely and let it come down to room temperature. Voila! soldered SMT parts.

It's a little noisy as the relay clacks on and off, and I need to figure out a clean way to attach the controller to the oven, but for now it works great.


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I need a bigger telescope 

The summer is flying by. I just got back from the 2010 Golden State Star Party (GSSP) up in Adin, California. Adin is a great little town, and the local people are super nice. GSSP is held on a few acres of Albaugh's Frosty Acres Ranch. The organizers do a great job of turning an empty cow pasture into a self contained astronomy encampment for four nights. The skies are incredibly dark. The site is on a bit of a rise in the middle of the "Big Valley", so you can see house lights some miles away. Once you realize how far away they are an just look up, you can practically read by the light of the Milky Way.

Here's a shot of my camp, complete with Orion 8" dob.

It's nice and cozy. The Aluminet provides much needed shade, especially when trying to sleep in after a long night of observing.

The problem is that there are some seriously big telescopes there: .

This one is a custom made 30" telescope. I can't really call it a dob, since money appeared to be no object in its construction. It is an alt-az mount, completely motorized and computerized for go-to operation. I left feeling quite inadequate in the aperture department. I wonder how much I can get away with spending on a bigger telescope before the spouse complains....

I'll be headed to Yosemite with the Sonoma County Astronomical Association in about a week. More great camping with telescopes!


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Monitoring WWVB 

I had a thought about monitoring WWVB on 60KHz the other day. Since I have a really stable source of time (GPS disciplined Rubidium Oscillator) why not log the phase of WWVB relative to the GPS time instead of monitoring the amplitude of the signal?

I can think of a few ways to do this that would be easy to implement:

1) Pure analog setup with a ramp and a sample/hold circuit
2) Frequency counter with a & b inputs to measure the time.
3) Microprocessor to measure the time difference.

Since I have a suitable counter, maybe I'll set up to watch the time difference over a few days to see how it looks before deciding on a final approach.

Thoughts anyone?


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Maker Faire 

I had a really nerdy weekend! I spent Saturday at the Maker Faire in San Mateo. I've been a big fan of Make magazine since it debuted, and I have been to all of the Bay Area Maker Faires. This year was really great. A mind-bending experience as always. Plenty of Steampunk, model rockets, trebuchets, mad science, tesla coils, robots, you name it. I highly recommend attending.

The other nerdy thing I did was to go to Sturgeon's mill, which is a steam powered saw mill in western Sonoma County. The mill has been on this spot since the 1920s. When it was shut down in about 1963, Wade Sturgeon, one of the original partners, continued living on the site. He had the foresight to keep the rain off the old mill, and to go out once a week with his oil can to keep everything lubed and moving. I wish more people could think ahead that way. Recently a group including Wade's family got together and brought it all back to life. When you stand on the deck as they saw logs, you can feel the pulse of the steam engine and hear the exhaust note change as the saw blade bites into the log. IT'S ALIVE!!!


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Decametric Receiver Mods 

I've been playing with the TenTec 1056 receiver to optimize its performance measuring solar noise. One of its features as a communications receiver is the fairly narrow and adjustable bandpass filter. The manual doesn't say, but it appears to have about a 1KHz bandwidth. This is really too tight for picking up broadband noise from the sun.

The guys at Fringe Dwellers recommend adding a switch to allow you to bypass the bandpass filter stage altogether. This goes a little too far the other way for my suburban location. The Radio Jove receiver has a multi-pole filter with a 3.5 KHz bandwidth. I decided to follow their lead. I put a simple RC filter in place and so far it seems to be working well.

Here's how it is hooked up. Remove the "Mute" jumper and put an SPDT switch across it with the common to the right end. Across R12 (3.3K), put a series combination of a 1K resistor with a 0.047uF cap. The resistor goes to the right, the other end of R12 is ground. The node where the resistor joins the cap connects to the other end of the bypass switch. Voila, a simple RC filter.

Now to record data for a couple of days and see how my results compare to others.


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