+ "description": "<p>This is a Digital Multimeter in the shape of an SAO (Shitty Add-On/Simple Add-on), designed specifically to assist in electronic badge and SAO development.</p><p>This follows the 1.69bis version of the SAO standard (<a href=\"https://hackaday.io/project/52950-shitty-add-ons\">Shitty Add-on standard</a>, <a href=\"https://hackaday.io/project/175182-simple-add-ons-sao\">Simple Add-on standard</a>)</p><p>It is based on the RP2040 chip, includes a small OLED display, a rotary encoder for the main knob, a function button for sub functionality selection and two 2mm banana terminals for connecting probes for resistance, LED and continuity testing.</p><p>A USB-C connector on the side allows easy modification of the firmware, and boot and reset buttons are also included for convenience, when updating or replacing CircuitPython.</p><p><strong>CAUTION! THIS IS NOT A NORMAL MULTIMETER, AND DOES NOT INCLUDE THE PROTECTION FEATURES NORMALLY FOUND IN A DMM</strong></p><p>If you would like to probe a live circuit, please check <a href=\"https://github.com/flummer/dmm-sao/blob/main/DMM%20SAO%20Schematics.pdf\">the schematic</a> first, and proceed only if you understand the implications, as improper use might result in a short circuit and harm either the multimeter, the device under test, a connected computer or a combination of those.</p><p><strong>VOLTAGE OR CURRENT SHOULD NEVER BE MEASURED WITH THE PROBES OR TERMINALS ON THE FRONT</strong></p><h2 id=\"features\">Features</h2><ul> <li>Resistance measurement (not the most precise, but should be OK in the range of 50-10K ohm)</li> <li>LED Tester (this will lit up the LED if the polarity is correct and show the voltage across it on the screen, 100 ohm resistor in series to 3.3v)</li> <li>Continuity tester with buzzer to indicate very low resistance</li> <li>Measurement of input voltage on the SAO port</li> <li>SAO Port GPIO monitoring (shown as either digital high/low or an analog voltage reading)</li> <li>I2C monitor (monitor or scan the I2C bus on the SAO port)</li></ul><h2 id=\"technical-details\">Technical Details</h2><ul> <li>Raspberry Pi RP2040 controller</li> <li>16MB SPI flash (W25Q128JVxQ)</li> <li>SSD1306 128x64 pixel 0.96” OLED display (white on black)</li> <li>Automatic power switching from SAO port to USB-C (both can be connected at the same time)</li> <li>Voltage boost circuit for operation on lower than 3.3v on the SAO port</li> <li>Maximum input voltage on the SAO port is 3.3v</li> <li>UART RX + TX connected to SBU pins on USB-C connector</li></ul><h2 id=\"links\">Links</h2><ul> <li><a href=\"https://hackaday.io/project/198892-sao-digital-multimeter\">hackaday.io page</a></li> <li><a href=\"https://github.com/flummer/dmm-sao\">Github repository</a></li></ul>"
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