Matthias' Blog

In this article, I will describe the operation of an I2C receiver built from discrete gates and components. The receiver has one register that can be read from and written to. Unlike other I2C devices, the contents of the register can be ORed or ANDed with another byte without reading and writing in separate transactions. The circuit described in this article is designed for slave devices that only accept data (for example, a motor driver) and do not return any data (for example, a temperature sensor). Modified I2C protocol Note: the protocol described in this section is not the same as the proper I2C protocol Clock signal (SCL) Unlike with true I2C, the clock signal SCL runs all the time. This provides all devices on the bus with a continuous clock signal. This allows other devices to transmit on the bus without having their own crystal or oscillator. Since the bitrate is 100kbps, but 200kHz is required for transmission, the two clock signals are mixed into one signal on one wi

In this post, I will describe three light timer circuits. These circuits all have a switch which is mechanically connected to a door and a light controlled by that switch in some way. Each circuit lights the light for a certain amount of time after the door is opened before switching it off. Circuit 1: installed August 2020 This circuit is based around an LED task light which had already been bought for the purpose of becoming a closet light. This LED light had a button for selecting the mode and a built-in rechargable lithium cell. However, the light had no motion sensor or door switch to turn it on automatically. Thus, a circuit was constructed to switch the light on when the door was opened. The schematic is shown below: Simulation of circuit The components inside the box represent part of the circuitry inside the LED light. In reality, the gate of the MOSFET is connected to a control circuit that can adjust the brightness of the LEDs. The 10k resistor was not originally in the

Recently I got a window-mount fan with two separate fans and several operating modes. The device has a built in temperature sensor and supposedly is able to switch the fan based on the termperature in the room. It has one button that cycles through all 13 modes: off, fan on high, fan on low, fan on high with thermostat set to 60, 65, 70, 75, or 80 °F, and fan on low with thermostat set to 60, 65, 70, 75, or 80 °F. I didn't test the thermostat modes, but I do not think they would have worked well because temperature sensor was located in the case and would have read a different temperature than if it had been further into the room. Additionally, the fan would be unable to tell whether switching on the fan would have increased or decreased the temperature and might have made the room warmer even if it wanted to cool the room. However, I liked the ability to adjust the speed (and thus the noise) of the fans. To make the fan easier to use, I first bypassed and removed the control circ