This circuit is for a superheterodyne receiver where the image frequency is suppressed without the use of an input filter. Instead, it uses two NE(SA)612 type mixer ICs that each work 90° ou... Read more
In microcontroller circuits, quartz crystals provide the highest accuracy for keeping everything on frequency. With frequency and time measurement (and for commissioning master clocks) fine... Read more
This RJ-45 cable tester automatically checks cable continuity and tests the connection configuration. Each of the eight connections is checked independently and short-circuits are detected.... Read more
In the decoder designed for the DTMF Link project, a Holtek HT9170B does the main job. The natural counterpart of the HT9200B used in the associated encoder (described elsewhere in this publ... Read more
This circuit has been designed to respond only to two hand claps which occur in (relatively) quick succession and to ignore one hand clap or even continuous clapping, as well as most other s... Read more
A bandpass filter is usually used to pass frequencies within a certain frequency range. If a high-performance opamp is used, such a filter can also be used at relatively high frequencies. As... Read more
Using just a few discrete components and two inverters, it is possible to build a simple TTL square wave frequency doubler for signals up to about 100 kHz. The input signal is applied to the... Read more
Instrumentation amplifier using an opamp An instrumentation amplifier is a kind of differential amplifier with additional input buffer stages. The addition of input buffer stages makes it ea... Read more
Voltage-operated switches are fairly commonplace but frequency-operated ones are still rare. The one described here is based on a 4046, a PLL (phase-locked loop) that, internally, is largely... Read more
This compact four-digit digital counter is suitable for any application, such as clocks, frequency meters, digital voltmeter, tachometers, stop-watches, scoreboards, etc. The counter module... Read more
