Drilling and populating the SUNDAR PCB

Last night I stopped at Harbor Freight and picked up a ‘set’ of solid carbide drills. To call them a set is a silly as each package has 20 random sized bits. But since the packaging is clear, you can select the grab-bag set that has the rough sizes you need. At home I was able to drill out the PCB for the few through hole parts without any bit breakage or copper tear-out. For $8 these bits were very cost effective.

After drilling I even had a few minutes to solder the SMT amplifier into place. I hope to fully populate the board over the next few days.

The reason I was unable to spend alot of time on the PCB was that I am preparing to teach a class in LEGO NXT-G programming this weekend. I had to clean up last year’s slides and start to duplicate 20 disks for the participants. Luckily I have the DVD robot that will double as an automated duplicator. Just load in a bunch of blank CDs, launch the application and come back a few hours later to a nice stack of burned disks. Sweet.

Posted in FIRST LEGO League, Robotic DVD burner, SUNDAR | 1 Comment

SUNDAR PCB using Press-and-Peel

I was unwilling to send out the PCB for the SUNDAR radar head to a fab house. I only need one and why spend precious money that I could use elsewhere. So I tried out the Press-and-Peel method for etching my own PCB. Turns out it was pretty simple and gave remarkly good results. Continue reading

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SUNDAR update #2

I took a few weeks off for vacation and to get my son ready to go to Europe for two years to complete his master’s program. I have a few things left to clean up before I can start back into my projects full time.

But I did get my son to teach me how to use Eagle while he was home. I was able to lay out the PCB for the rotating sensor head. This has the PIN diode, and the first stage transconductive amplifier. The output of this amp will transfer over the slip rings to the second gain/offset amp and the digitizing micro.

After printing the board full scale, I was shocked at just how small the dang thing is. The old fashioned Sharpie pen and/or rub-and-peel decals is not going to cut it. Most traces are 16 mils wide and the parts are all SMT.

I am going to attempt to make the board using press-and-peel blue film. If that does not work, I will try the photo sensitive boards that you expose using UV light. If both these methods fail, I guess I will have to send it out for fab, but I would rather be able to make one of a kind boards at home even if I need to invest in some equipment.

Hope to try the press-and-peel this weekend.

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SUNDAR update

Today I replaced the opamps with the new ones I just got from Analog Devices. These were SMT parts and I had to solder them to DIP adapters. But they share the same pin outs as a DIP, so the substitution was trivial. They work like a charm. I have now started to work on the mechanicals. Continue reading

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All is not lost with GPS

So after looking at the GPS data I collected, I figured I would try another data collection in 2D mode with the know altitude set. That would allow me to use one more satellite for horizontal position. I collected 12 hours of data and if was even worst than the 3D solution. So I got to thinking. Continue reading

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GPS error

Towards my goal of entering the AVC competition in 2014, I have been evaluating GPS units. The current model I am looking at is a u-Blox LEA-6H with a patch antenna. The first test I tried was to hold the GPS stationary and record data for 30 minutes. I recorded the North and East position and started analyzing it. What I found, I do not like. Continue reading

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A Storm!

Had a storm come through the area when I was at work. Luckily I had the Tautic board running and collecting data. I have just spent some time processing the data and I am now rather hopeful that this might work. Continue reading

Posted in Lightning detector, Projects | 2 Comments

AS3935 “Striker” software update

I was notified my Striker code on GitHub had a defect (bug). The contributor posted a patch that I have implemented.  You can find the updated code at www.github.com/skyesweeney/striker

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Opamp trouble

Been working on the two stage opamp for my Sundar. The first stage takes the current from the photodiode and turns it into a voltage with a certain amount of gain. The second stage applies a second gain as well as an offset via two digital (SPI) potentiometers.

The first set of opamps I uses were 741s I had around. They did not work because the need +-9V and I am running on a 5V rail. The next set I picked up from Radio Shack were a bit better but still were not rail to rail. Next set I ordered from Digikey were rated rail to rail in the title, but only later did I find out that was only the case for larger voltages.

Last set I am working on (again from digikey) was designed for low voltage but although the input is rated rail to rail, the output still is not.

So after careful consideration and talking to every EE I know, I placed an order for some expensive opamps from Linear Technologies. These are rated for a single 5V supply with railt to rail inputs and outputs. Hope these work when they arrive early next week.

Posted in AVC, Projects, SUNDAR | 2 Comments

SUNDAR update

Been working on my SUNDAR in what little free time I have these days. Last night my Digikey order came in and I was able to get the dual channel digital potentiometer working. This will be used for a software AGC type circuit to adjust the offset and gain of the light sensor amplifier. Continue reading

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