The Precision Low Frequency Signal Generator produces a User-selected signal from 10Hz to 90Hz with 0.1Hz resolution for testing subwoofer speakers. The frequency is displayed on a 16x2 LCD. The sine wave is produced by stepping through a table of 64 values and sending them to the MCP4921, a 12-bit serial DAC that uses an SPI interface. This is how to use the Precision Low Frequency Signal Generator. INC- Press and release to increase the frequency- Press and hold for about 2 seconds to keep increasing the frequency; release to stop DEC- Press and release to decrement the frequency- Press and hold for about 2 seconds to keep decreasing the frequency; release to stop MODE- Press and release to toggle the frequency step between 0.1 Hz and 1.0 Hz- Press and hold for about 2 seconds (then release) to enter Sweep mode at 0.1 Hz increments- When in Sweep mode Press and hold for about 2 seconds (then release) to exit Sweep mode The skill level for stuffing the board is: Intermediate. Make sure you use a temperature-controlled soldering iron. I use a temperature of 340 degrees Celsius. And don’t inhale the solder fumes. If you don’t have a fume hood use a fan to blow the solder fumes away from you. To compile the source code and download it into the microcontrollers I use Texas Instruments Code Composer Studio. It is free and is on this page: https://www.ti.com/tool/MSP-EXP430G2ET where you can get the versions for Windows, Linux and macOS. The direct link to the current version for Windows is: https://software-dl.ti.com/ccs/esd/CCSv10/CCS_10_4_0/exports/CCS10.4.0.00006_win64.zip . The skill level to use Code Composer Studio is: Advanced. (Maybe Really Advanced). Notes: 1. You can use an MCP4921 in the PDIP package or the SOIC (SMD) version. 2. To program the MSG430G2402 you connect the Precision Low Frequency Signal Generator to the Launchpad with three wires. To make it run standalone remove the three wires and use a header plug to connect the /RES and /Reset pins on the header (on the Signal Generator). 3. The audio outputs are: Line Level, Speaker, and Speaker Test. The Speaker Test has a 100 Ohm resister in series for testing speakers. The testing of subwoofer speakers and the design of subwoofer cabinets is beyond the scope of this article. I recommend the following: 1. For testing subwoofer speakers to derive the Thiele-Small (TS) parameters: Measuring Loudspeaker Parameters by Rod Elliotthttps://sound-au.com/tsp.htm Basically, you: a. Connect the Precision Low Frequency Signal Generator to the subwoofer speaker through the onboard 100 Ohm resistor. This makes the output a current source. You will need a sensitive voltmeter with a good low frequency response or you can use my companion project: Woof Meter which contains a low frequency preamp, a precision full-wave rectifier, and a DC filter. It has a voltage output that can be read with any standard DC meter. It also has a current output for use with an analog 1mA meter. b. Find the free air resonant frequency of the speaker. That is where the voltage across the speaker is at a maximum. c. Find the higher and lower frequencies where the response is down 3dB. That is 0.707 of the voltage (or current) at resonance. d. Add a weight of 25 grams to the speaker cone. A U.S. nickel weighs exactly 5.0000 grams so tape 5 nickels onto the cone. (Use masking tape.) e. Repeat the above tests: find the resonant frequency and the two -3dB frequencies. f. There are other things for you to measure (with a standard multimeter). g. Plug your measurements into the proper formulas and you will get the TS parameters. Then you can design the cabinet. 2. For designing subwoofer cabinets for vented, sealed, and custom bandpass cabinets: https://www.ajdesigner.com/speaker/ . Also see: http://www.mh-audio.nl/Loudspeakers.html#top I live at an altitude of about 6,000 feet. I designed the Precision Low Frequency Signal Generator to see how the altitude affects the TS parameters of a subwoofer. To do that I put the subwoofer in a 55 gallon drum and pressurized it in stages down to sea level.I have posted more information (which you need) and more pictures on my Web site: www.jmargolin.com/newprojects/woof-tester/woof-tester.htm This includes the source code. The source code is complete. It does not require any libraries other than the ones that come in Code Composer Studio. Happy Subwoofer testing and building. Jed MargolinVirginia City HighlandsStorey CountyNevada11/8/2021

The ULX3S is a fully open source, compact, robust and affordable FPGA board equipped with a balanced spectrum of extra components and expansions. Although primarily developed as a teaching tool for mastering the principles of digital circuit design 1, a wide selection of useful features and interfaces enables it to serve as a broad spectrum module for installation in complex devices.ULX3S uses powerful Lattice Semiconductor ECP5 series FPGA chip supported by the latest open-source toolchains. This makes the ULX3S one of the most powerful and desirable platforms for FPGA enthusiasts available today. ULX3S comes equipped with onboard WiFi, display, buttons, LEDs and storage. Flash it using the WiFi connection (over-the-air update), or with one of the bitstreams stored on SD card and browsed by onboard OLED display and buttons. Due to its battery-backed RTC, it can power down completely and wake up only on certain events making it useful for low power applications such as battery-powered remote sensor nodes. And if you’re not of the low-power type, onboard peripherals such as SDRAM, USB, Digital video out, onboard FM/ASK antenna, ADC and DAC can make it audio/video powerhouse for signal processing and synthesis, motor control or SDR cases. You can emulate arcade machines or retro computers like Minimig(Amiga) or modern systems like F32C (MIPS/RISCV). It has 56 GPIO pins, all routed as differential pairs and a PMOD compatible pinout, opening it to a wide range of expansion options. If you are just starting with FPGA, you can also use the ULX3S as powerful Arduino and program it using Arduino IDE in seconds.It has been actively developed since 2016 and is the result of collaboration between Radiona.org / Zagreb Makerspace and FER – Faculty of Electrical Engineering and Computing – University of Zagreb, Croatia.1 ULX3S is being actively used in Digital Logic class at the University of Zagreb Faculty of Electrical Engineering and Computing, Croatia

Project BackgroundI am very fascinated by technology since my childhood. I like working with electronic gadgets and I am very keen in developing things on my own. Hence, I decided to design a circuit based on the ESP32 IoT development module.Circuit DesignThis circuit consists of a ESP32 development board, a soil moisture sensor and an OLED display. The ESP32 module powers up both the Sensor and the display.The soil moisture sensor has 2 probes attached to it. These probes go into the soil. These sense the moisture content and returns an Analog value. This analog value goes to the ESP32. The OLED display works on I2C protocol. It is connected to the SCL and SDA pins of the ESP32. The OLED displays the Moisture value in Percentage(%).The advantage of using the ESP32 is that it being a WiFi module, we can connect it with Digital Cloud and store data. We can also access the data wirelessly. This system is very useful in agriculture as the farmer can access the soil moisture content data from anywhere.Video

Regular solder paste dispensers must be connected to compressed air which you can provide with huge compressor. As a maker I can not run a large compressor in my room because of its noise and footprint.Stencils might be a solution but for small size PCB work they are too dirty and I don't like to touch the chemical solder paste with my hands and with my tools. It takes more time to clean up everything than apply it to the PCB.That's why I decided to design a desktop solder paste dispenser that is clean, easy to use and small in size. I called it Solderocket.Using the rotary knobs, the time and pressure can be set so that the right dot size can be selected for each type of solder paste.This device is indispensable when working with SMD on a regular basis. SMD paste can be dosed very accurately and quickly. Adhesives can be used in addition to SMD paste.