Thursday, September 14, 2017

A SI5351 VFO-BFO UPDATE 9/15 9/16

Working on Pete's Simpleceiver + I need to build another VFO BFO.  The SI5351 based boards have been my favorite for several years now.  I have several different versions of boards that I have tried, but prefer the small module from Adafruit.  It is very small, and comes built for around $8 plus shipping.  One of the things I like about it is that the clock outputs are brought out to a header along with the SMA connectors.  I have used this board in several projects and have designed different boards for each one.  With this I plan on designing a board that can be used with many different projects.
The design considerations are, board size around 2" x 2",
Arduino Nano, rotary encoder, TFT display, a connector for the Adafruit SI5351 board. After an initial design and exchanging several e-mails with Pete I have expanded it to also provide a connector for a small  I2C OLED display.  Because there are several pinouts for these displays, some will plug in directly to the connector others will have to use a connector cable to the display. This connector could also be used to connect to a I2C version of a 1x16 or 2x16  line LCD display. With the correct software drivers you could use one of these LCD displays, a small OLED display, a 128x128 or 128x160 TFT display, or even a monochrome Nokia display.    I also added a connector that brings the rotary encoder connections out to a separate connector so you can  use either the bare encoder mounted on board, or one of the pre-wired encoder boards. I have not tried but you could probably use an optical encoder through this connector. 
One thing I added was provisions for a voltage divider that can be used to measure input voltage if the board is used in a battery powered project. Finally I decided to bring some of the unused Arduino pins out to an auxiliary connector for use in other projects.

Since the board layout is similar to several others I have done, I was able to modify one of them fairly quickly.  I did the board as a single sided board that can easily be made using the "toner transfer" method.  Although I usually etch my own boards, in this case I decided to order some from one of the inexpensive Chinese board houses.  If they turn out well, I will follow Pete's suggestion and make some available at a reasonable cost for those who are working on the Simpleceiver or other project that needs a VFO-BFO.  I think I will start with one of these boards as the basis of a simple signal generator for routine use.  This should be a easy way to test the different video drivers needed for the different display options available.

I ordered the boards on Sept 9 with DHL express delivery, and was pleasantly surprised when I received them on the 13th.  I quickly wired one of them up to see how they will work.  Changing some of my other sketches to reflect the correct pin configuration I tried the board with a small OLED display and a 128x128 TFT display. After getting a working display with each, I was sure that the board worked correctly. 
I installed a right angle female header strip so I could mount an external rotary encoder board, and took some pictures of possible display configurations. There are several more that I could try, but this is what I had handy.
I also took a picture of the Adafruit SI5351 board mounted on the back.  Depending on how the header pins are installed in the board, it can also be flipped to have the edge with the SMA connectors extending past the board edge.  I planned on the Nano and SI5351 board to be soldered to the board, but they could be socketed if you do not need to keep everything really compact.  As it is with everything soldered the package with the OLED or 128x128 TFT is about 2"x 2"x 1".  This should be small enough to fit in most project packages.  Now to write some software to fully test each of these configurations

I had some time today, so I took Pete's Simpleceiver Plus DCR sketch and modified it to reflect the changes in the pin assignments on the new board.  And after I had it working with the 160x128 TFT display I modified that to reflect the 128x128 display.  There are several different versions of the 128x128 display that use different driver chips, so I had to also change the driver library and initialization code. With a little tweaking on position on the display I was able to get a very similar looking display screen. I had taken all of the additional code in the sketch that reflects U/L side band selection and several other things that Pete has in his code to make it more modular in design.  When I get around to going to a superhet and then transceiver, these can be added in as separate .ino files in the main sketch directory.  That way it should be possible that no other changes in the additional .ino files should be necessary whatever display you are using.  Here are a couple pictures of the two displays.  Hope to get around to writing some code for a couple other display types this weekend.

128 x 128 display  Rotary encoder on board

160 x 128 display  External rotary encoder

I spent a little over an hour this evening modifying one of the earlier sketches to support a small 0.96" OLED display.  Most of that time was trying to fit everything on the screen, and make it look nice.  It is much easier to work with a screen that has more real estate to work with. This is listed as a two color display, but all pixels are either white or black, the color comes from  two different colored parts of the screen.  In an earlier project, I used the smaller color area to put current settings.  

One thing to be very careful about when using these small OLED displays is that looking at some of the pinouts for ones for sale on ebay, is that some have the VCC and GND pins reversed.  
SO BE VERY CAREFUL and check before just plugging it in the socket.  I still have one of the monochrome Nokia displays around, but with the problem I had trying to fit everything on the screen, I don't know if I will bother porting the code for that configuration.

Now that I know the boards work for multiple display types, I have decided that I will offer them for sale.  Because of Pete's urging, I ordered 50 of them to start with.  For now I only plan on shipping to US locations, but am working on getting the board layout as a shared project at the Chinese board house I used. This should make it easier for DX locations to order them directly.  I had checked at, but the board size made them rather expensive.  The board is single sided, so fairly easy to make with the "toner transfer method" if you want to make your own.  I will have the "toner transfer" image along with other documentation at

This dropbox will also have the Arduino sketches to use as a guide in using the board with different types of display.  They are very rough right now, I just did enough work on them to get the display and rotary encoder to work correctly.  I will be doing a lot of work as I progress with the Simpleceiver project and see what Pete has in store for us.

I am offering them at $5 each or $7.50 for two including shipping. If you are interested email me at and I will give put you on the list.  

I have just uploaded the files for this board to the supplier I used to their shared projects area.  You can download the gerber files from there or order directly.  I have placed several orders with this supplier, and have been very happy with the results.  Their pricing is very reasonable, and they offer several different shipping options that can be very reasonable. This will be the most economical way for DX builders to purchase boards. The project is at

And yes I do get a commission from boards sold. So if two people buy  sets of  5 boards I save enough on my next order that I can stop at McDonalds and get a cup of coffee when it is on sale.

Saturday, September 2, 2017

Simpleceiver Circuit boards

I have received several e-mails with questions about the boards I am making for Pete's Simpleceiver project.  I use a layout method known as "Muppet" style.  This is well documented by a series of YouTube videos by Chuck K7QO.  The first of his 12 videos covering design, layout, etching, and building is  at

The boards are laid out using the free "expressPCB" software, this is about the easiest to learn PCB software I have found.  Since it was made to be layout software for a single board house, it does have some limitations compared to other programs.  But, for making simple "toner transfer" boards it is more than adequate.
I have made a few changes to Chuck's procedure for board layout. The main change has been to modify several of the component foot prints that comes with the software, to provide large mounting pads instead of the through hole pads provided.  
I find it much easier to grab the correct Muppet component from the custom list and place them where I want. These  have a outline of the component over the pads, which makes it much easier to follow the circuit diagram.  I have pads for the common resistors, capacitors, diodes, transistors, and IC sockets I use most of the time.  Any other can be built from standard pads as required.  This also makes it easy to mix through hole components along with standard size SMD components if I am laying out a SMD board.

Since the "Muppet" board is etched on the top layer of the PCB, it is necessary to flip the image right to left for proper transfer. Chuck prints the top layer image to a PDF and then uses a linux program to flip it.  I found another program "Copper Connection" that will import expressPCB files and then print both sides in the correct orientation for "toner transfer" or photographic method.  It also has some nice features that I sometime use to help with the board layout.  One of them is to flip a board over when doing double sided boards.  Unfortunately it is now hard to find a copy of this software after they were bought out by expressPCB.

Another change is the "toner transfer" method I use.  Chuck goes through a great explanation of the "Hot" method using a laminator. I have found that the results of this method is very dependent on the brand of printer used and if you use OEM or generic replacement toner.  After seeing another method on a internet site, I switched over to the "Cold" method.  This uses a chemical solution to soften the toner, and then the image is pressed onto the blank circuit board.  I found that I can get much more consistent results using this method, than I could with the "Hot" method.  I have slightly changed this by passing the board and image through my laminator without first waiting for it to warm up.  This seems to give more even adhesion of the toner than just pressure alone.  I usually pass the board and image through the laminator from several directions to give even adhesion.  This works much better for larger and double sided boards.  I have a blog entry that describes my method and another later one that covers how I make double sided boards.

After completing the layout for the LM380 audio amplifier and the product detector, I decided to combine them into a single board.  I found that I could open one of the files in expressPCB software, highlight the area I wanted to copy and copy to the clipbaord.  Then open the second file and paste the first into it.  Then I used the software to reposition components or 
add/delete traces as necessary. 

Last evening I also finished up 
the SMD version layout in two different size formats.
I have a SMD board ready to etch, and hopefully I will be able to get that done tomorrow.

Update 9/4/17
Well I etched the board, and of course I found an error I had caused when I rotated a section of the board around.  I  made some quick changes, and etched another one. Then built the AF amplifier half of the board, so I can test it without having to worry about any noise or issues introduced by the product detector circuit. Very pleased with the way it turned out.  Since I had coated the board with a thin coat of lacquer after I etched it, the only problem I had was trying to get a good picture without a lot of glare off of the board. 

I hope to get time tomorrow to do some testing on the amplifier and check what the frequency response is, and how much gain I get out of it.