Etching a Breakout Board for SC70-6 and DFN-6 Footprints

 

A while ago I took an interest in experimenting with digital pots and caps. So I ordered the MCP4018 and the NCD2400.

The package size should prove to be a bit of a challenge, especially the NCD2400 which comes as a DFN-6. The MCP4018 is SC-70-6 which should be ok.

While I didn’t have the correct breakout boards for either chip, I could have made do with what I had on hand for the 4018. But there was nothing I had on hand for the NCD2400. So, I decided to try and see if I had the skills to etch my own breakout boards that small.

My 1^st attempt (upper left in picture) resulted in a board that while it had no shorts, it was not suitable. The iron was to hot and or I pressed to hard.  My 2^nd attempt (upper right in picture) was better, from the perspective of the board quality and I reworked the trace sizes somewhat. The traces leading up to the IC footprint were wider and then reduced leading to the component. The thickness there was the same size as the pin on the chip.  However the board was still not good enough to attempt to solder the chips in place.

My 3^rd attempt proved much better. Traces were altered further as well and I made the attempt to solder the chips in place.

The 4018 install went fine, a little crooked but there were no shorts and that's what counts for the moment.  But, the 2400 was a different story.  I tried the tin one pad and reheat the pin and follow up with the rest method, but after a few unsuccessful attempts the trace lifted.

I’m not sure how exactly my next approach to solder a DFN IC will be but I’m still confident I can do it without the use of a solder oven. I do have parts on hand to make a solder oven but who knows if and when I’ll build it.

The MCP4018 is working well and I am experimenting with it at the moment with the UA741 opamp. That will be a posting at a later date.

 

 

A Few New/Old Projects on the Go.

 

I am always amazed at how one project can lead to several more.  The latest example of this for me was the Signal Generator project my HB Club undertook last year. 

Once that project was completed, I wanted to be able to control the output. So that lead to incorporating the PE4302 step attenuator chip and how to use it. 

Next was instead of calibrating the SigGen and then selecting an output and calculate the output level, I wanted to measure and display the actual reading.  I also wanted to be able to read at least to one decimal point. This led to exploring an alternative to the Arduino Map function and experimenting with a 16bit ADC, ADS1115 chip. It also has led to utilizing an opamp on the output of the AD8307 and seeing if that can help in reading accuracy especially in the area of the 2^nd decimal point reading.

Of course, it does not stop there as now I needed to better understand how I2C communications worked.

With all the different boards laying about and a too numerous to count number of interconnecting cables, test leads, power leads, erratic and intermittent performance, I needed to build a test bed.  So here was another project that this time didn’t contribute directly to the project, but I did end up with a good test bed for any future Arduino projects.

In the Altoids tin is the AD8307 board. Opamp to the immediate left and further left is the ADS1115 and Si5351 boards.  The 2 Nanos, LCDs, ADS1115, and Si5351 boards are all connected via I2C. 

More details to follow shortly about how all this pans out.   

Signl Generator Control Project Update

The software development had been taking up a fair bit of my time mainly because I really don't know a whole lot about Arduino coding and hacking into the existing code for the original SigGen was a bit daunting. Fortunately Kevin, VE3KHH who is doing the same project as I am, has the appropriate skills for the software changes and gave me a few clues on how to approach this. His end of the software changes is completed and I still have a bit of work left to do on the rf sensing code.

I took a break from software to start assembling all the various boards into a repurposed power supply case.

Since the nano for the step attenuator was now redundant, the code is now in the SigGen Nano, I removed the existing pin headers for the nano and installed new ones on the reverse side of the board. I used headers to access the the encoder and the 2 attenuator boards.  I needed to add in a 3.3vdc power supply for the attenuators as the nano was no longer installed. I mounted the regulator right on some unused pins. Unfortunately I let the smoke out of the 1st regulator. I forgot that the tab was also Vout and had soldered it to ground. Good thing I always order several components at a time so I have a few spares.

If all goes well I should be able to disassemble everything and paint the case sometime next week. 

Thought Experiments are Good With the Right Tools:)

Change of Pace. Lets try operating cw.

Decided to change things up and actually do some operating instead of building. 

A few of local area hams got together the other night and dusted off older QRP CW rigs and see what happens.  In my case I used an all homebrew station.

My setup consisted of an all hb tuner and audio filter. The keyer and rig are kits. Still hb in my eyes.

CW was rusty, as expected but I did well enough that the Reverse Beacon Network picked up my 2 watts. My signal was heard state side in 1, 8 , and 9 areas.  But the band was very busy and was barely heard at times locally. Need a little more power for the ground wave stuff.

Anyway it was fun and will give it another go but I'll likely use my KX3instead.

Signal Generator Control Project

Looking for a simple project to work on, I decided to revisit the signal generator project that I did as part of the Peel Amateur Radio HB Group. That build took place several months ago and at the time the specs for the project did not include any control over the output voltage levels.  I was always going to address that issue and this seemed to be the perfect time to do so.

I built a step attenuator, highlighted in 2 previous posts,  and quite some time ago I experimented with the AD8307 logarithmic amplifier chip and have a couple of prototype circuits for measuring low power signals sitting around in the junk box. I have the prototype SigGen as well the Arduino board I used for those experiments was still in one piece with the original program. So, why not put all the pieces together and see what happens. 

A quick assembly of the various boards and run through shows some promise but its obvious some work to optimize the code will be necessary. Another issue that has become a bit obvious is how to assemble all this in under one box.

The SigGen uses a Nano and I'm wondering if I can fit the code for the 8307 into that program and that way I can eliminate an Arduino. Space is tight in the Nano but the 8307 code is not huge. Time will tell.

From left to right, the SigGen, Step Attenuator, AD8307 board, and the Arduino running the RF measurement program.

 

Nano Controlled Step Attenuator Pt 2

Finished the project today. At least as far as getting the board to work. Still need to think about how I'm going to package it up.

I did a quick scan of the attenuator from 1Hz to 2gHz and looks to be pretty flat . But I'm not all that interested in such high frequencies so I concentrated 1Hz to 50mHz.

There is about a 2.5dB insertion loss and stepping through at 10dB steps up to 60dB shows a linear plot of 2.8dB on top of the dialed in attenuation. In other words, add 2.8dB to the dialed in setting. Exception however was found at 50mHz where it was 2.4dB.

I think I'll adjust the code in order to take into account the insertion loss so what you see is what you get. No need to do math in the head, as easy as it is. I'm sure I'll be busy concentrating on other things while using the attenuator.

Back To Basics

Time to get back to some basics so I built a direct conversion receiver. The design is based on the MRX40 Mini Receiver by K8IDN.

I did not use a crystal that was used in the original design and used my homebrew signal generator instead. I removed all components associated with the crystal circuit except for the capacitor across pins 6 and 7 of the SA612 mixer.

I ended up removing the 220uf capacitor on the output of the regulator as it was shorting to ground.  Fortunately not enough smoke was let out of the regulator that it quit working. Got very very hot though. Another self inflected problem was during the initial power up and testing I used a signal generator to supply the signal source. What I didn't anticipate was that signal was strong enough that it ended up blowing the LM380 chip. I had another one on hand and lowering the source down to an appropriate level proved the circuit worked. 

The receiver worked great and pulled in signals on the 40m band better than expected. Bench testing showed I could an injected signal down to the -120dBm area.