Circuits & Schematics Security

Many electronic-control systems have digital outputs that use transistors. One method of improving the security in these outputs is to use an oscillating signal to represent a logic-high state instead of a fixed voltage level (Figure 1). This type ...

You can use the circuit in Figure 1 to monitor the rotating speed of a dc fan motor and sound an alarm if the motor stalls. One potential application of the circuit is monitoring the CPU-fan speed in a PC in which overheating the CPU can ruin the ...

The residual-current circuit breaker in Figure 1 continuously monitors the supply lines for any leakage current and immediately disconnects the supply if necessary. Load-supply wires, both live and neutral, pass through the magnetic core of the ...

Maxwell Strange EDN Figure 1 is the block diagram of an easily programmed, single-button combination lock. You operate the lock by using a series of short and long pulses from a momentary switch that masquerades as a doorbell button. The circuit ...

Bert Henscheid Electronic Design While creating an infrared beam intrusion detector system, the need for a beam-focusing method became evident. Parts from a modified Genie garage door Safe-T-Beam system, purchased at the local home improvement ...

Jeff Tregre EDN Shortly after installation, the simple water-leak-detector circuit in this Design Idea saved the day and hundreds of dollars. The average life expectancy of a hot-water heater is about 10 years. It’s not a question of whether ...

While most carbon dioxide sensors use IR technology, electrochemical sensors are a serious competitor because of their high sensitivity, wide measurement range, and low price. As a rule, electrochemical sensors connect to a microcontroller through ...

Although piezoelectric elements have been used for shock and vibration detection for some time, this circuit provides a low-cost alternative for solid-state general-purpose impact sensing. The circuit uses a standard piezoelectric device ( PZT ) to ...

Introduction This RFID reader works with 125 kHz tags in credit card size shape cards and with 125 kHz key fobs (Figure 1). The EM4100 protocol is used. When you approach an RFID Tag close enough (4-5 cm) to the reader's coil (L1) the reader will ...

This shield could be used as a stand-alone transponder key, or with Google’s servers to create a cloud-computing application. It’s time to present you an application with RFID. We want to show you how to use the popular Arduino to ...