AT89S51 Programming Schematic

The AT89Sxx learning board features,

•     Designed for new ISP chips, 89S51, 89S52, and 89S53, 40-pin DIP,
•     In System Programmable (ISP) through the 6-pin header and a jumper, (no need external programmer),
•     TxD and RxD serial port for communicating with serial devices,
•     32 bit GPIO,
•     Onboard rectifier and +5V DC voltage regulator,
•     Single Sided PCB design.

Simple Audio Limiter Schematic

Technical specifications
Supply voltage: 10-14 V stab.
Supply currents: 20 mA
Audio input: impedance 20 kOhm, optional preemphasis
Output voltage: 0,4 V rms
Dynamic range: >50 dB

High Quality 60 Watt 8 Ohms Power Amplifier Schematic

 

Basic Uninterruptible Power Supply (UPS)

This circuit is a simple form of the commercial UPS, the circuit provides a constant regulated 5 Volt output and an unregulated 12 Volt supply. In the event of electrical supply line failure the battery takes over, with no spikes on the regulated supply.

1 GHz Frequency Counter

This simple counter is useful for frequency measurements of various wireless equipments, especially transmitters, receivers and signal generators in VHF/UHF band.

Features

• Display range: 0,0 to 999,9 MHz, resolution 0,1 MHz
• Correct rounding, reduced blinking of last digit
• Over-range indication
• Fast measurement - short measuring period
• High input sensitivity in VHF/UHF band
• Switchable intermediate frequency offset for use with receiver
• Technical specifications

Level indicator with 10 LED

Technical specifications:

• Supply voltage: 12 V
• Supply current: 10 mA in stand-by, max. 80 mA
• Input voltage: min. 20 mV rms
• Indication range: 30 dB
• LED currents: 7 mA
• Ref. voltage of IC2: 5 V