Hall Effect

An alternative approach for this application takes advantage of low-offset op-amp characteristics to design a circuit that works with a wide voltage range and needs no other supply. The V+ and inverting and noninverting terminals of the OP07 op amp need a minimum of approximately 2 to 2.5V to function properly. Thus, you can pull the op amp`s inputs by more than 2.5V below the positive-supply connection and tie the op amp`s V+ pin to shunt V+ (Figure 2)..

Hall-effect sensors are preferable for speeds of several pulses per second, but they require the attachment of a magnet to the rotating assembly. They`re thus prone to failure when the magnet is broken or damaged. Neither variable-reluctance nor Hall-effect sensors offers fail-safe detection of the processed signal in the event of failure in the cable or sensor. The circuit in Figure 1 is a fail-safe variable-reluctance sensor for low- to medium-speed operation...

The circuit in Figure 1 provides a way to check a battery`s condition. Measuring a battery`s voltage is not the best way to check its condition; it`s better to measure the power that the battery delivers in a discharge process to evaluate the battery`s energy capacity and life. The circuit in Figure 1 discharges a battery in a constant-power mode. You can select the level of discharge power. The GMR sensor`s output signal is related to the discharge power. The power stage uses a bipolar Darlington transistor, which draws little power from its op-amp driver. You place the GMR sensor over the pc-board trace that connects the Darlington`s emitter to ground...

The 12 Volt power in my application comes from a small solar power system, it may also be provided by a suitable wall-wart DC power supply. The cistern is located below the toilet tank, the pump moves the water up to the toilet`s tank. The pump is switched on when the toilet tank is empty, it is switched off when the tank has filled...

Half of the effort in this project was to achieve the original timing. When I removed the old coils from the stator poles, I concluded that the timing signal was coming from this pole. The coil that was on this pole had many turns of very fine wire, hardly enough to drive the 0.2 ohm resistance of the special factory ignition coil. So I concluded that its signal was what signalled the original ignition module to trigger spark. So I shaved about a 1/16" off of the pole with my dremel, and used a dab of JB-Quick epoxy to fasten the hall effect sensor to the end of the pole, taking care to maintain that close `dollar bill` clearance to the flywheel magnets...

Have you ever wanted to find out how strong a magnet really was, or how the strength of the magnetic field varied as you changed the distance from the magnet or the temperature of the magnet, or how well a shield placed in front of the magnet worked? Voltmeters are fairly inexpensive and easy to find, but where do you purchase a Gaussmeter (also known as a magnetometer). I built a hand-held Gaussmeter for measuring the polarity and strength of a magnetic field. It uses a linear Hall effect device and some op-amps and resistors and things from Radio Shack...