$5 junkbox Circuit Determines Phase Sequence :  04/23/98 EDN-Design Ideas / (added 10/05) [Note:  File contains multiple circuits - scroll to find this circuit.]  Have you ever wondered which way a blower motor is going to turn when you plug it into another socket, or have you ever inherited the task of modifying three-phase wiring in your plant? The circuit in Figure 1 is a simple, approximately $5 phase sequencer that you can probably build from parts in your junk box and save approximately $50 to boot. The component values reflect 60-Hz operation, but the design equations in Figures 2 and 3 allow you to select values for other frequencies. The equations are in MathCAD spreadsheet format, but almost any other spreadsheet would do...

60 Hz modulator records process variables :  02/16/98 EDN-Design Ideas  / (added 11/05)   The circuit in Figure 1 allows you to record process variables (4 to 20 mA, 0 to 10V dc) on a three-phase power monitor designed to record only ac waveforms. Many of these recorders have a seventh channel, normally used for recording neutral current, which you can use as a process-variable input. The circuit operates by generating a 0 to 1V-rms output sine wave whose amplitude is a function of a 0 to 10V-dc input signal. IC1 can be any rail-to-rail quad op amp rated for ±5V power supplies. Input stage IC1A buffers the input-voltage divider R1-R2 and drives the two-quadrant multiplier, IC1B. IC1B acts as a multiplier by using Q1 to switch its gain from 1 to 1....

Circuit eases three-phase monitoring :  12/17/98 EDN-Design Ideas  / (Circuit / schematic design added 6/06)    Measuring line-to-line voltages in a delta-connected three-phase system can present special problems. Because all three lines may be floating several hundred volts above ground, you can not use nonisolated, grounded oscilloscopes or other single-ended instruments. Special isolation amplifiers are available for oscilloscopes, but they can cost several thousand dollars. You still need to make three measurements even with proper instrumentation. The circuit in Figure 1 reduces the magnitude of the line-to-line voltages and combines them into one ground-referenced signal (Figure 2) that you can safely monitor with a grounded oscilloscope....

Inverters form three phase VCO:  08/02/01 EDN Design Ideas  /  (added 1/05)  You sometimes need an inexpensive VCO that can produce evenly spaced three-phase outputs over a wide frequency range. You could use tracking all-phase filters with only one oscillator, but this technique is difficult to implement and offers limited range. Other methods, such as using a DSP, are feasible, but they're complex and expensive....

Level shifting nixes need for dual Power Supply:  01/06/00 EDN-Design Ideas / (added 09/05) The AD736 true-rms-to-dcconverter is useful for many applications that require precise calculation of the rms value of a waveform. This converter can determine the true rms value, the average rectified value, or the absolute value of a myriad input wavefo...

Optocoupler simplifies Power line monitoring:  01/10/02 EDN Design Ideas  /  (added 1/05)  The use of a linear optocoupler and a capacitor-based power supply yields a simple, yet precise power-line-monitoring system. The circuit in Figure 1 converts the 110V-ac power-line voltage to an ac output voltage centered at 2.5V, covering 0 to 5V. The circuit isolates the output signal from the power line. ...

RF Transmitter uses AMI encoding:  11/24/99 EDN-Design Ideas / (added 8/03) Although alternate-mark-inversion (AMI) encoding is well-suited for direct-conversion FM transmission, designers often overlook the technique. AMI, a three-phase, synchronous-encoding technique, uses bipolar pulses to represent logic ones and no signal to...

Self modifying code extends addressing mode:  12/17/98 EDN-Design Ideas  / (Schematic / circuit design added 08/05)   As just about any assembly-language programmer knows, self-modifying code (SMC) is usually undesirable, unintentional, and destructive. However, the SMC routine in Listing 1 is extremely useful to extend the indexed, 16-bit offset addressing mode of the venerable HC05 µC from 8 bits, or 256 locations, to the full 13-bit (8-kbyte) memory address space that the µC’s architecture supports. This routine is very useful for error tables, text messages tables, or any array manipulation for a large number of elements....

Three phase Power Supply:  The "small" three phase power supply is capable of delivering 3.5 kV at 1 A. The 380 V AC is connected via a start-up circuit, limiting the initial current. It is a temporary power supply, used until the final one is ready. (Electronic circuit design added 02/05)