Homebrew 500 watt HF power amplifier

Jeff (K6JCA) has written a series of posts describing his homebrew project 500 watt HF power amplifier:

I started this project back in 2016 — I had finished my Automatic Antenna Tuner (seen in the upper-left of the picture, above) and a PA project that would integrate into my FPGA-SDR and ATU system seemed like the ideal next step.
While researching RF amplifiers, I discovered a Microsemi App Note, “A 700W Broadband Amplifier using VRF2944”. I decided to use its design as the basis of my PA and began gathering parts.

See the full post on K6JCA blog.

How to make analog sensor readings with digital I/O pins

Edward Mallon wrote an article describing a technique he used to make analog sensor readings with digital I/O pins:

Will this method replace our pin-toggled oversampling? Perhaps not for something as simple as a thermistor since that method has already proven itself in the real world, and I don’t really have anything better to do with A6 & A7. And oversampling still has the advantage of being simultaneously available on all the analog inputs, while the ICU is a limited resource. Given the high resolution that’s potentially available with the Timer1/ICU combination, I might save this method for sensors with less dynamic range. I already have some ideas there and, of course, lots more testing to do before I figure out if there are other problems related to this new method. I still haven’t determined what the long-term drift is with our Pro Mini clones, and the WDT experiment taught me to be cautious about counting those chickens.

See the full post at thecavepearlproject.org.

Teardown of an Amrel PPS 35-2 programmable power supply

Kerry D. Wong did teardown on a single-channel Amrel PPS 35-2 programmable power supply:

A while back, I did a teardown on a dual-channel Amrel PPS-2322 programmable power supply, and was quite impressed by its solid construction. Recently, I found another Amrel power supply on eBay and this time it is a single channel version (PPS 35-2). Let’s take a look inside this signal channel version and see how much in common it has compared to the dual channel 2322.
The single channel version of the Amrel programmable power supply has front panel sensing terminals making it handy for remote sensing applications. Although the dual channel version has remote sensing capability as well it is only available through wiring at the rear terminal block so it is less convenient.

More details on Kerry D. Wong blog. You can see the teardown of an PPS 2322 dual channel power supply here.

Check out the video after the break.

Continue reading “Teardown of an Amrel PPS 35-2 programmable power supply”

#FreePCB via Twitter to 2 random RTs

Every Tuesday we give away two coupons for the free PCB drawer via Twitter. This post was announced on Twitter, and in 24 hours we’ll send coupon codes to two random retweeters. Don’t forget there’s free PCBs three times a every week:

  • Hate Twitter and Facebook? Free PCB Sunday is the classic PCB giveaway. Catch it every Sunday, right here on the blog
  • Tweet-a-PCB Tuesday. Follow us and get boards in 144 characters or less
  • Facebook PCB Friday. Free PCBs will be your friend for the weekend

Some stuff:

  • Yes, we’ll mail it anywhere in the world!
  • Check out how we mail PCBs worldwide video.
  • We’ll contact you via Twitter with a coupon code for the PCB drawer.
  • Limit one PCB per address per month please.
  • Like everything else on this site, PCBs are offered without warranty.

We try to stagger free PCB posts so every time zone has a chance to participate, but the best way to see it first is to subscribe to the RSS feed, follow us on Twitter, or like us on Facebook.



Bus Pirate “Ultra”: using ADS7042 12bit Analog to Digital Converter from the FPGA

Beginning with Bus Pirate “Ultra” prototype v1d, all analog measurements are handled by the FPGA using an external serial Analog to Digital Converter chip. This lets us pipeline ADC measurements into the command queue so that bus interactions can be done with very precise timing.

ADS7042 pins. Source: ADS7042 datasheet page 6.

We’ll be using Texas Instruments’ series of tiny ADCs with a max speed of 1MSPS: the ADS7041 (10bit) and ADS7042 (12bit). For the prototype we went with the 12bit version, but availability and final BOM price will dictate what goes into the final design.

ADS7042 sampling interface timing. Source: ADS7042 datasheet page 10.

The ADC uses a dead simple three wire interface that resembles SPI without a Master Out Slave In connection. CS falls, the first two clock ticks are 0, then the next 12 bits are the analog voltage measurement. We stripped down a copy of our Verilog SPI peripheral to drive the chip, the current source is here.

ADS7042 calibration interface timing. Source: ADS7042 datasheet page 24.

There are two methods of calibrating the ADC. Offset calibration can be done immediately after power up by sending 16 clock ticks, however it’s risky to depend on the ADC being in the reset state. Calibration can also be done at any time by sending 32 clock ticks, which is the method we used.

Bus Pirate “d” command retrieves the ADC value through the FPGA

This is a very basic test that retrieves the raw ADC value from the FPGA while measuring the programmable output power supply voltage.

In the final revision, absolutely every aspect of the Bus Pirate hardware front end will be controlled from the FPGA:

  • IO pins (added in v1a)
  • Logic analyzer and SRAMs (added in v1a)
  • Analog voltage measurement (added in v1d)
  • Pull-up resistors (added in v1d)
  • Programmable output power supply (to be completed in v1e)

It’s possible we might use a 3.0volt reference for the analog section on the next revision. Currently we can measure 0-6.6volts with a divide-by-two resistor divider and a 3.3volt referent. A 3.0volt reference gives a 0-6volt measurement range, which increases the resolution over our target range of 0-5ish volts and might mean we can use a cheaper, lower resolution ADC. The Digital to Analog Converter used in the power supply has almost no noise rejection, so a dedicated reference voltage would help ensure clean DAC output as well.

App note: Keys to high flexibility

Ever wonder why some wires used on moving attachments last long? Cicoil who innovate the flat ribbon cable has done a lot since early computers on hi-flex wires. Link here

Most industrial wire is made up of multiple wire strands, called ‘base strands’, rather than being made of a solid piece of metal. Multiple strands make the wire more flexible, allowing it to bend and flex more easily than solid metal.

App note: Insulating and Jacketing Materials

Different application calls for different insulations, heres a great info on different insulation and jacketing materials from Calmont wire & cable Inc. Link here

Today’s wire user has a wide range of plastic insulating materials to choose from, and yet the selection of a particular dielectric for a specific application frequently is a trade-off in properties. Each plastic has both desirable characteristics and practical limitations, and the user must decide what can be sacrificed to assure overall satisfactory service.

Free PCB coupon via Facebook to 2 random commenters

Every Friday we give away some extra PCBs via Facebook. This post was announced on Facebook, and on Monday we’ll send coupon codes to two random commenters. The coupon code usually go to Facebook ‘Other’ Messages Folder . More PCBs via Twitter on Tuesday and the blog every Sunday. Don’t forget there’s free PCBs three times every week:

Some stuff:

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Custom NES cartridge – Harambe’s revenge

Troy Denton and Brad Taylor made a USB reprogrammable NES cartridge:

Initially, Brad and I wanted to make a PCB that could do some very ambitious things, requiring either a very capable processor, or an FPGA device. We began down this path, but soon realized that we were biting off much more than we could chew for something we had never done before. So, we decided to take a step back, and make a smaller project to verify the foundations of our design. Our final design goals were:
*Be programmable via USB
*Be able to play NROM format games
*Feature nonvolatile storage (no battery required)
*Be as cheap and easy to manufacture as possible

Check out the video after the break.

Project info at troydenton.ca.

Continue reading “Custom NES cartridge – Harambe’s revenge”

Monitoring GNSS constellations with Galmon using the LimeNET Micro Ublox-M8 module

Luigi Freitas (PU2SPY) writes:

In this blog post, I will explain how I managed to get a GNSS multi-constellation monitor called Galmon working on my LimeNET Micro. The Galmon project is a crowdsourcing tool developed by @PowerDNS_Bert to monitor the health status of GNSS constellations including the GPS, GLONASS, BeiDou and more notably Galileo. The project relies on volunteers to set up inexpensive stations based on the Ublox-M8 module to receive GNSS packets and send diagnostic data back to an aggregator.

More details at luigifreitas.me.

ESP32 LoRa sensor monitoring with web server (Long Range Communication)

Rui Santos posted detailed instructions of how to build an ESP32 LoRa sensor monitoring with web server:

In this project, you’ll build a sensor monitoring system using a TTGO LoRa32 SX1276 OLED board that sends temperature, humidity and pressure readings via LoRa radio to an ESP32 LoRa receiver. The receiver displays the latest sensor readings on a web server.

Check out the video after the break.

Project info at randomnerdtutorials.com.

Bus Pirate Ultra 2.8 inch display and the danger of Taobao suppliers

We’ve been prototyping the Bus Pirate Ultra with a 240 x 320 pixel 2 inch LCD, but it’s just a bit small and hard to read from a distance. A 2.8 inch version is available that fits the full width of the Bus Pirate PCB, with the trade off of bigger pixels/lower pixel density. We bought a few displays from various “manufacturers” on Taobao and made up a daughterboard. It failed spectacularly because the datasheet was so wrong!

Anode and cathode pin locations in the “datasheet”
Anode and cathode position on the actual display

We don’t have to go beyond pin 1 to find a major and obvious error. The datasheet lists pin 1 as the LED backlight anode, and pins 2-5 as the cathode. The printing on the flex connector makes it clear that four cathodes (K1-4) join into a single trace to pin 1. A single anode (A) trace connects to four pads on the connector (pins 2-5). The backlight connections are backwards.

Coincidentally, datasheets for other similar displays (2.8 inch, 50 pin connector) match the corrected pinout. This datasheet just had it backwards. We reversed the backlight power and ground on the PCB by drilling out a trace and creating some strategic solder bridges. While the LEDs light, the display doesn’t respond to any commands so other connections could be wrong.

That’s not all. The flex cable is actually several millimeters shorter than listed in the datasheet, so it can’t reach the connector through the slot in the daughterboard.

We had similar issues with this supplier’s 2 inch display. The dimensions in the datasheet are a bit off, and their sample initialization code doesn’t work. We asked for an updated datasheet and received three different versions, none of which matched the actual display.

Their Taobao page has pictures of a factory and a nice section on after sales support. A charitable guess is that they manufacture runs of custom displays, and sell the excess on Taobao. That would explain all the different datasheets they so readily have available. We tried to get another grab-bag of PDFs for the 2.8 inch display, one of which might match the actual pinout, but at this point they got tired and ghosted us.

Will we stop buying prototyping samples on Taobao and 1688? Definitely not! It’s a great way to see what’s a cheap commodity product. This process plays out in the Shenzhen markets as well, people sell a lot of stuff without knowing exactly what it is. It’s kind of up to us to know what we’re buying, and sometimes it’s a crapshoot. When we find a sample we like, it’s time to send someone up to the factory to meet the boss, drink way too much tea, and ensure we’ll have a steady and consistent supply in the future.

#FreePCB via Twitter to 2 random RTs

Every Tuesday we give away two coupons for the free PCB drawer via Twitter. This post was announced on Twitter, and in 24 hours we’ll send coupon codes to two random retweeters. Don’t forget there’s free PCBs three times a every week:

  • Hate Twitter and Facebook? Free PCB Sunday is the classic PCB giveaway. Catch it every Sunday, right here on the blog
  • Tweet-a-PCB Tuesday. Follow us and get boards in 144 characters or less
  • Facebook PCB Friday. Free PCBs will be your friend for the weekend

Some stuff:

  • Yes, we’ll mail it anywhere in the world!
  • Check out how we mail PCBs worldwide video.
  • We’ll contact you via Twitter with a coupon code for the PCB drawer.
  • Limit one PCB per address per month please.
  • Like everything else on this site, PCBs are offered without warranty.

We try to stagger free PCB posts so every time zone has a chance to participate, but the best way to see it first is to subscribe to the RSS feed, follow us on Twitter, or like us on Facebook.



Understanding and repairing the power supply from a 1969 analog computer

Ken Shirriff writes:

We recently started restoring a vintage1 analog computer. Unlike a digital computer that represents numbers with discrete binary values, an analog computer performs computations using physical, continuously changeable values such as voltages. Since the accuracy of the results depends on the accuracy of these voltages, a precision power supply is critical in an analog computer. This blog post discusses how this computer’s power supply works, and how we fixed a problem with it. This is the second post in the series; the first post discussed the precision op amps in the computer.

More details at righto.com.

Bus Pirate Ultra prototype v1d: the last alpha

Bus Pirate “Ultra” v1d is stuffed and about half tested. This should be the last alpha “figuring out if we can pull this off” version. New in this revision:

Analog voltage measurement is now done from the FPGA using a 12bit 1 million samples per second ADS7042 Analog to Digital Converter. This will let us pipeline voltage measurement commands with other bus commands and reduce dependency on any specific MCU.

The programmable output power supply is now controlled by a DAC104S085CIMM Digital to Analog Converter chip, instead of the DAC in the MCU. This further reduces our dependency on a specific MCU, and will later allow us to control the voltage regulator from the command pipeline in the FPGA. It may be possible to simulate different power supply conditions and glitches, for example.

A lot more thought went into the programmable output power supply. V1d measures current through a shunt resistor, and we added a small load to test it. There’s several other goodies in there, but we’ll reveal them later.

In addition to sampling voltages on each IO pin from the FPGA, we’re now sampling several other voltages from around the board (power supply output, current consumption, etc) . We swapped the 8 channel 74HCT4051 analog multiplexer with a 74HCT4067 16 channel multiplexer. This part of the board needs some more thought because some of the voltages would be better measured without the divide by 2 resistor divider currently used after the op-amp.

The display daughter board now uses a 0.5mm pitch flex connector. We though these connectors and the flex cables would be a nightmare to work with, but they’re actually a lot of fun. They’re really compact too.

After a little more testing we’ll get to work on v1e, which should be the first beta and possibly the first version ready for a small production run. Find the latest updates and follow a group build of v1d in the forum.

Drive an MCP49XX series DAC with an AVR ATmega

Davide Gironi writes:

Driving that IC is pretty simple, expecially if you have a dedicated SPI hardware interface, like many microchip has.
The ATmega8, used in this example has a dedicated SPI Control Register (SPSR) that one can use to setup the SPI interface.
This library can drive more then one MCP49XX of the same series at the same time, this is done just by selecting the chip using a SS channel for each one.

See the full post on his blog.

Check out the video after the break.

Continue reading “Drive an MCP49XX series DAC with an AVR ATmega”