I haven’t had time to update the blog because I’ve been busy designing a new headphone amplifier. There’s been a lot of development when it comes to operational amplifiers and I was curious about how well I can get an amplifier to measure using the latest technology. The op amp I’m using still hasn’t got a development board, so I make one myself. The op amps are 5x5mm in PVQFN-20, so you need to use an SMD soldering gun or oven to be able to solder them. I simulated the circuit with both LTSpice and TINA90, but left biasing resistors and some other stuff in good old fashion though-hole components for easy testing.
DIY Reference 10 MHz Distribution Amplifier
I wanted to get a distribution amplifier for my 10 MHz lab reference signal from my GPSDO to feed my equipment, like my timer/frequency counter, signal generator, and other stuff. I also needed a way to distribute a 1 PPS signal from my Trimble GPSDO to my NTP servers and other clocks and monitoring systems. The Trimble only got two 10 MHz outputs and one 1 PPS signal output, so I needed to add more, especially for experimentation.
I saw this video by Gerry Sweeney where he modifies an Extron 300MX video distributions amplifier, adding a rubidium reference standard and was intrigued. But I changed the modifications to fit my needs and here is the result.
Philips-Fluke PM6665 Frequency Counter with Oven Controlled Crystal Oscillator
Upgrading a Philips-Fluke PM6665 Frequency Counter with an Oven Controlled Crystal Oscillator – Up and Running!
I needed a frequency counter for my little lab at home. Naturally, I wanted an HP Agilent 53132A or similar, but it’s way too expensive for my modest use. So I browsed around eBay and found an old Philips-Fluke PM6665 frequency counter with the optional 1.3GHz add-on board. With a 10 second gate time, I can get down to 0.1 Hz at 10 MHz, so that’s more than I need. It didn’t have the option of a better crystal, unfortunately. When I tested the PM6665 against my Trimble 10 MHz GPSDO reference, the unit was off by 200.1 Hz. Without a calibration sticker on the instrument, I’d say that’s pretty good for a device manufactured in the late 80s. I tried to trim it, but it uses an adjustable capacitor, and you only needed to look at it for it to change settings.
Speeding up your SPI MAX7219 LED displays using a modified Arduino LedControl Library
Speeding up your SPI MAX7219 LED displays when using Arduino and LedControl Library
In preparation for the arrival of my GPSDO[1], I’m doing a quick build of an “Atomic Clock” display to have above my lab equipment. I’m using a cheap, small eight digit red LED SPI-controlled display. It uses the MAX7219 controller that I got from eBay for next to nothing. I plan to parse the RS232 information from the GPSDO unit and display the exact time. I’ll also post error messages if the GPS signal lock gets lost.
I’ve done a quick prototype using an Arduino Uno, but I plan to try to get an Attiny85 to work as the controller when I’ve finished the parser and the rest of the software.
After doing some research, naturally, there was a library available to connect to my LED display called LedControl. It’s part of the standard Arduino libraries (in the download section). But when I checked the code, it uses the Arduino routines to shift out the SPI data to the display. It’s great if you want to be able to use any pins to connect to the screen, but using Arduino’s bit manipulation tools for “bit-banging” the display is slow.
Upgrading a Philips/Fluke PM6665 Frequency Counter with an Oven Controlled Crystal Oscillator OCXO
I’ve finished the OCXO upgrade. Read about it here
While browsing on eBay for my new lab at home (I’m getting into electronics again), I came across a Philips PM6665 Frequency Counter, an old but functional unit so I couldn’t resist, I had to buy it. So I downloaded the Users Manual and Service Manual for the frequency counter and started to check the schematic. As usual the unit, when new, could be bought with several options. One of them was a better crystal oscillator, an MTCXO that can be automatically calibrated using a 10 MHz external reference, giving an accuracy of 3*10-8 but my unit doesn’t have that option, unfortunately. This will be fixed though. But it does have a 70 MHz to 1.3 GHz optional input!
So here’s what I plan to do…
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