PV Solar Cell Test Fixture  -  This is an illustration of a test fixture, which can be used to test individual solar cells for short circuit current. Using a PIN photo diode and a control circuit, the solar cells can be tested under constant light level conditions . . . [Hobby Circuit designed by David Johnson P.E.,  10/01/06]

PWM controller drives LEDs from high-voltage lines  -  03/04/04  EDN Design Idea   Powering LEDs from a wide dc range—say, 30 to 380V—without wasting a lot of power in the regulating block, is a difficult task when the LED current needs to be constant. Dedicated LED drivers are available, but they usually implement. . .  [by Christophe Basso, On Semiconductor, Toulouse, France]

PWM IC makes synchronous gate driver  -  02/02/99 EDN Design Idea (contains several designs, scroll to find this one)   A system with a µP, memory, and peripherals usually requires several power-supply voltages. Designers typically use local switching regulators to produce the desired voltage rails. One of the most common topologies, the synchronous buck regulator, converts a 5 or 12V bus to some other, lower voltage. . .  [by Dimitry Goder, Switch Power Inc, Campbell, CA]

R/C Model Aircraft Marker Light Flasher  (ATTINY12 and others)  -  The lightest weight solution I could come up with, uses just about any AVR controller. You can even do it with a PIC!. . .  [From Dick Cappels' project pages]

Radio Tower Lamp Monitor  -  The circuit below uses two 3 Amp diodes to produce a fairly constant 2 volts whenever current is routed to the tower lamp. The voltage is used to power a bright LED. The LED will only turn on when current is actually flowing to the lamp. With the component values shown, the circuit will work with lamps ranging from 40 to 250 watts.  . . . [Hobby Circuit designed by David Johnson P.E.,  07/18/06]

RainboW LED indicates voltage with color  -  12/07/04  EDN Design Idea   Meters that indicate analog levels via a moving-pointer meter, a numeric display, or a column of LEDs typically occupy considerable panel area and require than a casual glance to read. An indicator lamp or LED takes little space but . . .  [by David Prutchi, Impulse Dynamics, Haifa, Israel]

Ramping Lamp Driver  -  This circuit drives any 12v lamp, incandescent or LED type, in a ramping fashion. Each press of the button toggles the lamp from a fully off mode to a fully on mode. But, instead of an instantaneous lamp intensity change, the power is slowly ramped up a . . . [Hobby Circuit designed by David A. Johnson P.E.,  12/21/07]

Ramping LED Driver  -  The circuit below was designed to drive a LED with an intensity ramping mode. Two 555 timers generate two different triangle waveforms. The upper device generates a 10KHz signal while the lower unit produces a 1Hz signal. The two signals are fed to a . . . [Circuit by David Johnson P.E.,  12/21/07]

Rapidly Stops DC Motor Drive   -  This circuit will bring a fast moving DC motor to a stop in seconds. The braking action is automatically applied whenever DC power is removed . . . [Circuit by David A. Johnson P.E.,  09/25/04]

Really Loud Output Beeper Circuit  -  I you need a real loud beeper, this circuit delivers about 110db (12 inches away) from a 9v battery using a single inexpensive C-MOS IC. An off-the-shelf piezoelectric beeping device is driven at resonance to insure maximum efficiency. By changing the control IC to a 74AC14, the same circuit can operate from 3v and 1. 5v batteries . . . [Hobby Circuit designed by Dave Johnson P.E.,  06/03/00]

Red LEDs Function As Light Sensors  -  03/20/08  EDN Design Idea   You can build simple LED illuminators using the red LED to sense ambient-light level. . .  [by Geoff Nicholls, Glinde, Germany]

Reduced Power Relay Driver  -  Relays can handle a lot of power. However, for certain power sensitive designs you would like to reduce the power needed to hold a relay closed. The circuit below performs such a task. It uses a single CD4093 quad NAND gate. When the “on” logic input . . . [Circuit by Dave Johnson P.E.,  08/03/08]

Reduced Power Sequential LED Flasher  -  The 74HC4017 is a neat decade counter which has 10 decoded outputs. When supplied with a low frequency clock and with a LED attached to each of the outputs, an interesting ten step sequential flasher effect can be produced. The LEDs can be configured in . . . [Hobby Circuit designed by David Johnson P.E.,  11/30/08]

Relay Driver  -  A relay is an electro-magnetic switch which is useful if you want to use a low voltage circuit to switch on and off a light bulb (or anything else) connected to the 220v mains supply. The diagram below shows a typical relay (with "normally-open" contacts). . . .  [© David Hoult 2013]

Relay driver saves substantial power  -  07/02/98 EDN Design Idea   (File has several circuits, please scroll to find this one. )It is common practice to operate relays and solenoids at a reduced holding power once the mechanical actuation takes place. Relays are usually specified to pull in wit. . .  [by Tim Herklots, Maxim Integrated Products, Southamption, UK]

Relay Driver Switches Two Relays With One Pin  -  03/03/11  EDN Design Idea   Logic 1, logic 0, and high-Z make for three possible states: forward, reverse, and off. . .  [by Gunther Kraut, PhD, Egmating, Germany]

Relay Driver with Reduced Power  -  Relays can handle a lot of power. However, for certain power sensitive designs you would like to reduce the power needed to hold a relay closed. The circuit below performs such a task. It uses a single CD4093 quad NAND gate. When the “on” logic input . . . [Hobby Circuit designed by Dave Johnson P.E.,  08/03/08]

Relay driver, transistorised  -  . . .  [Page's Author: Richard Torrens]

Relay logic: Startt/Stop buttons  -  . . .  [Page's Author: Richard Torrens]

Remote LED Indicator Light  -  There are times when you would like to transmit a signal from one LED indicator light to second LED at another location. The circuit below works well for this application. It takes advantage of the fact that the internal infrared LED inside an opto-isolator . . . [Circuit by Dave Johnson P.E.,  12/28/08]

Remote Relay Driver  -  I received a call from a Discover Circuits visitor who wanted a simple way to turn on an outside lighting system using a low voltage control line.   I suggested the simple circuit below.   The circuit is powered by a 9v battery and uses a very efficient latching relay.   Two low voltage wires lead from the a toggle switch to the remote relay.   A toggle switch selects either the on or off condition of the relay.   The relay contacts are rated at 10 Amps, so the small relay can handle a sizeable amount of power.  . . . [Circuit by David A. Johnson P.E.,  04/06/14]

Rolled-Off Noise Source  -  This is a circuit that generates white noise, rolled-off to drive earphones or a small speaker. White noise creates is a "rushing" sound, which sounds something like air rushing by your ear (s). White noise would be flat with frequency, . . .  [From Dick Cappels' project pages]

RS232c Line Driver IC Drives Power MOSFETs  -  10/24/96 EDN Design Idea   Easy to affect an interface between power MOSFETs and TTL circuits. . .  [by Santosh Shetty, NCRA, Pune University, Pune, India]

RS422 Converter for Minilogger  -  Build a simple line driver/reciever that meets RS422A for the MiniLogger V1. 0. Place a distant Minilogger and communicate over a full duplex serial line. . . .  [Wichit Sirichote, designer]

RTTY Terminal unit  -  This circuit may be connected directly across your rig speaker terminal and used to drive a teleprinter coil directly. A normal teleprinter coil requires 80/80 volts to energise the coil, but this is connected in series with a 2. 7K resistor to give a sort of constant current. The teleprinter coil never has more than 20 volts accross it, . . .  [from Harry Lythall's website]

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