New Circuits

A thermostat doesn't try to maintain a constant temperature. In order to do so - it would have to keep switching on and off every few seconds. Instead - it keeps the temperature within a specific range. When the preset temperature has been reached - it switches off. And it only switches on again - when there has been a significant change in temperature.

Pushing the button once will energize the relay. Pushing the same button a second time will de-energize the relay. Any simple momentary action push-to-make switch will do.

In this circuit a non-locking push switch is used to activate a load. The load remains switched on until power is removed from the circuit. The load is represented by R5 and D1, but could be a lamp, a relay or another circuit. S2 breaks power to the circuit but could be omitted altogether. If S2 is left out, then reset would be by disconnecting the power; this would mean unplugging the battery if battery powered or disconnecting from the electrical outlet.

An AC triggered switch for low frequency signals. This is a basic ac voltage operated switch made from discrete components. Both Q1 and Q2 work as common emitter amplifiers, but the biasing of Q1 is arranged by R3 and R4 so that about 0.5V is applied to its base; so with no input signal both transistors and the load is off.

This simple circuit will energize and de-energize a relay at the push of a button. Any type of momentary action push-to-make switch can be used. Pushing the button once - will energize the relay. And pushing it a second time - will de-energize the relay

The first circuit energizes the relay when the temperature rises above the preset level. The second circuit energizes the relay when the temperature falls below the preset level. The two circuits are practically identical. The only difference between them is the polarity of the transistor. The value of the thermistor is not critical. The important thing is the voltage on pins 5 & 6. Any value thermistor should work satisfactorily. But you may need to change the value of R1 - to achieve the desired range of adjustment.

The schmitt trigger circuit is built around a single LM741 op-amp, its output buffered by a transistor, which in turn energizes a relay. The relay may be replaced by a red LED if desired. The LM741 may be replaced by a LF411 or other JFET input op-amp with better slewing characteristics.

The first circuit energizes the relay when the light rises above the preset level. The second circuit energizes the relay when the light falls below the preset level. The two circuits are practically identical. The only difference between them is the polarity of the transistor. The value of the LDR is not critical. The important thing is the voltage on pins 5 & 6. Any value LDR should work satisfactorily. But you may need to change the value of R1 - to achieve the desired range of adjustment.

A Coil Coupled Operation Metal Detector made from readily obtainable components and using an ordinary medium receiver as a detector. The metal detector shown here may well represent a new genre. At any rate, after some exposure, it is regarded as such by those who have seen it. It is based on a standard transformer coupled oscillator (TCO) - hence the name Coil Coupled Operation (CCO) Metal Detector.

I tried to design a timer that would do everything it needed to do but with the smallest number of pieces and simplest mode of operation. It only needs the PIC, a four digit LED display, one other IC, a resistor network, one pushbutton switch and a capacitor. It can run on batteries if you use a solid state relay to turn the exposure light on and off thereby adding a minimum of parts to make a fully functional darkroom timer. A simple regulator would add only a few extra parts and allow the use of a "wall-wart" for power.

I just finished a half duplex serial asynchronous link from a simple PIC circuit to the RCX. It is able to receive codes from the RCX (or Lego RCX remote control) store them in RAM & EEPROM and transmit any IR op-code to the RCX in turn. Included in the firmware is a routine that takes any opcode(s) and expand it to the proper IR packet for transmission to the RCX. I've used the UIRT circuit with a few modifications for the hardware. The UIRT includes a serial port programmer for the PIC16F84A so you won't need a separate programmer.

An opto-interrupter made with Lego beams, regular parts, a 6 hole pulley wheel and an axle.

The Generator cell must have reasonable surface area on the Plates to generate a reasonable amount of Hydrogen/Oxygen. And a Typical construction would use Stainless Steel for the Electrodes to prevent them from being Quickly eaten away.

Back in the 1970's these were popular and the colored bulbs were typically place in a box with a sheet of "rippled/bubbled" Plastic in front to break up the light patterns. Some units gave very impressive light patterns. Using an LM324, this circuit has 3 active filters for low, medium and high frequencies. Trimpots are initally used to set the 3 filters to equal ranges. A Master control is than used to set for various volume levels.

A Very Simple circuit and some Variations. Play with it. All parts are cheap and should be easily obtained. None are very critical.

The Clock Controller was designed to be an exemplary of using 'C' language to control timer0interrupt, 7-segment LED and keypad scanning. It provides 1-bit sink currentdriving output, for driving a relay, opto-triac, say. Many projects requiring7-segment display and keypad interfacing may get the idea from the Clockcircuit and software.

No description available.

A very simple Preamplifier.

Well, it's pretty much a PAiA preamp - usual input circuity followed by one half of dual op-amp rigged in fixed 20dB amplification circuity, followed by second stage which is adjustable for up to 40dB amplification, for up to 60dB total. The power supply is a simple affair, supplying +-12V using 7912 and 7812 regulators. As ECM8000 is happy with only 15 volts of phantom power, I added a 7805 which I referred to +12V instead of ground - resulting in 17V output which I used for phantom power.

The bat ultrasounds are picked up by the microphone SPKR1 and go through two stages of amplification at Q1 and Q2. Separately, a tunable (R12) single frequency is produced by the LM567 oscillator U1. The LM567 is a tone decoder but here its input is grounded and its voltage controlled oscillator is used as a precision oscillator.