Unused 8051 pin gets assignment

In an 8051-based system without external program memory, the program-store enable (PSEN) pin is useless. However, you can indirectly control this pin using software. To do so, you execute the move-constant- (MOVC-) instruction-implementing table look-up. By accessing locations in external program memory (which is actually nonexistent), you can produce pulses on the PSEN line without disturbing program flow. Although you need a register for storing output data, you don’t have to install a decoder.
source:http://edn.com/archives/1996/010496/01di7.htm

A serial to parallel converter using the AT89C2051

The example program included with the PG2051 evaluation kit is a basic serial to parallel converter written in 8051 assembler. This is probably a good example of the uses to which an AT89C2051 can be put - it would be hard to get a serial to parallel converter much simpler than the single 20 pin IC in this circuit. The program is meant to serve as a useful example of 8051 serial routines and other programming, whether or not you actually need a serial to parallel converter.
Source: http://airborn.com.au/serial/sertopar.html

Accelerometer Schematic

Below is a rough schematic of the layout of the accelerometer PC board looking from the component side. The microcontroller is an Atmel AT89S8252, an 8051 clone. This microcontroller is in-circuit programmable using an SPI interface. The SPI pins are also used to drive the MMC. To permit the dual use there is a jumper block (located below the 74AHC244, marked "P" and "R") that allows the pins to be connected for programming (P) or running the code (R).
Source:http://www.randomuseless.info/accelerometer/schematic/schematic.html

Combine two 8-bit outputs to make one 16-bit DAC

Inexpensive, 16-bit, monolithic DACs can serve almost all applications. However, some applications require unconventional approaches. This Design Idea design concerns circuitry I recently designed for a tunable-diode laser spectrometer for a Mars-exploration application. The control circuitry included two 16-bit DACs that interface to the radiation-hardened, 8051-variant 69RH051A microcontroller.
Source:http://www.edn.com/article/CA454640.html

MIDI Drum Machine Project

The MIDI Drum Machine began in the Fall of 1991 as a project for a microprocessor system design course, shortly after I wrote PAULMON1, the 8051 monitor/debugger. A friend, Rod Seely, both a musician and electronics hobbiest suggested I design something using the Musical Instrument Device Interface, MIDI, that would be COOL and would work together with his collection of MIDI keyboards and synthesizers. Of course, I wanted to build something that could end up as a finished commercial product.
Source :http://www.pjrc.com/tech/midi-drums/drum-intro.html

Low-Cost Anemometer Fights Dust

This application note describes a low-cost circuit that can detect when a chassis fan filter has become clogged with dust. It does this by using a temperature sensor to determine the rate of cooling of a transistor in the air path of the cooling fan, thereby implementing a simple thermal anemometer.

source: http://pdfserv.maxim-ic.com/en/an/AN844.pdf

LX1970 VISIBLE LIGHT SENSOR

The LX1970 light sensor can be used in conjunction with an LCD Front or Back Light Controller such as the LX1992 for LEDs or the LX1689 for CCFLs. This application note describes how to design in the LX1970.

Source: http://www.microsemi.com/micnotes/1403.pdf

AM portable radio receiver by ZN414 IC

An AM portable radio receiver made from the ZN414 IC. The ZN414 ic has now been replaced by the MK484 which is identical in performance and pinout.

Read More

Micro Power AM Broadcast Transmitter

In this circuit, a 74HC14 hex Schmitt trigger inverter is used as a square wave oscillator to drive a small signal transistor in a class C amplifier configuration. The oscillator frequency can be either fixed by a crystal or made adjustable (VFO) with a capacitor/resistor combination. A 100pF capacitor is used in place of the crystal for VFO operation. Amplitude modulation is accomplished with a second transistor that controls the DC voltage to the output stage.


Read more

LM3647 Reference Design

The LM3647 provides a single-chip charge management solution for Nickel Cadmium, Nickel Metal Hydride and Lithium-Ion cells. The device handles the entire charging process from rejuvenating deeply discharged cells to providing a number of charge termination and maintenance options. The LM3647 Demo Board allows users to create a battery charging solution with little effort.

Link : http://www.national.com/an/AN/AN-1165.pdf

7.2 Volt Field Charger

The unit is novel as it’s display graph shows you the time the battery has been charging in 2 minute intervals up to 16 minutes when finished.... read more

Self-heated transistor digitizes airflow

A sensitive and reliable way to measure airflow is to exploit the predictable relationship between airspeed and the heat dissipated by a sensor exposed to the flow while being held at a constant temperature differential above ambient. The power required to maintain the elevated sensor temperature is proportional to the square root of the airspeed (King's law). The popular hot-wire anemometer uses this principle, but suffers from the disadvantage of using a relatively fragile airflow sensor, a thin metallic filament.

Link source: http://www.edn.com/archives/1996/031496/06di3.htm
Thank : www.next.gr

Transistor and FVCs make linear anemometer

A previous Design Idea presented a simple flow-to-frequency transducer that easily fits into mP-based measurement systems (Reference 1). You can accumulate and linearize its frequency output by using software without the need for ancillary circuitry. In other applications, however, you might prefer a linearized analog output.

Link source : http://www.edn.com/archives/1996/092696/20di4.htm
Thank www.next.gr

12-bit converter upgrades µC's ADC

The simple circuit in Fig 1 and an accompanying software routine let you easily substitute a multichannel 12-bit ADC for the 8-bit ADC internal to the 87C752 µC. A single assembly can then implement both the low- and high-performance version of a system. A socket lets you plug in the external ADC when you need it; otherwise, you plug in the network of 10 100V resistors. At power-up, the µC executes a routine that looks for the external converter.

Source Link : http://www.edn.com/archives/1994/070794/14di5.htm

18-bit ADC uses PC's serial port

A PC usually requires a plug-in ADC card to process analog signals. However, with the circuitry in Figure 1, a PC can communicate with an 18-bit ADC through its serial port. The port provides both positive and negative power supplies as well as control signals. IC1 is an 18-bit MAX132 ADC with a serial interface. It requires three input control signals, , DIN, and SCLK, and emits serial data, DOUT, and EOC (end-of-conversion) signals.

Source Link : http://www.edn.com/article/CA159691.html

2-channel ADC tags its own output

The circuit in Fig 1 shows a simple way to operate a 1-MHz, 12-bit ADC (IC1) in DMA mode while alternating between its two analog-input channels. The converter operates continuously, driven by the 1-MHz clock on the S/H input. Tying RD and CS low ensures that data are always present on the ADC's output bus. The outputs of the 74HC74 flip-flop, IC2, change state on the rising edge of the end-of-conversion (EOC) signal.

Source Link : http://www.edn.com/archives/1994/042894/09di4.htm

4-bit µP's A/D converter decodes keypad's inputs

Fig 1 shows a Mitsubishi M50927-XXXSP/FP 4-bit microcontroller decoding a 4×4 keypad using only four digital I/O lines instead of eight. Saving four of a 4-bit µC's precious I/O lines couild be significant. The 4-bit µC's ADC provides the key to the savings. The µC's output lines, F1 through F4, energize the keypad's column lines one at a time via 74HC4049 buffer/ driver. If a user presses a key, the µC's ADC reads an analog voltage coresponding to the row of the pressed key.

Link Source:http://www.edn.com/archives/1994/101394/21di6.htm

DPP adds versatility to VFC

The basic VFC (voltage-to-frequency converter) in Figure 1 comprises an integrator (IC1) and a Schmitt-trigger circuit (IC2). The integrator converts the dc input voltage, VIN, to a linear voltage ramp, and the Schmitt trigger sets the limits of the integrator's output voltage. Feedback around both circuits provides the condition for oscillation. The DPP (digitally programmable potentiometer) in Figure 2 adds programmable limits to the Schmitt trigger and adds two powerful features to the VFC.

Source: http://www.edn.com/article/CA257049.html

40KHz Voltage to Frequency Converter

This circuit was designed to frequency modulate a 40KHz carrier, using human voice frequencies. A common flip/flop is used at the core of the circuit.

Source:http://www.discovercircuits.com/DJ-Circuits/vco1.htm

Voltage Monitor by 741

Parts List

D1 LED
R1 1.2k Resistor
R2 10k Var. Resistor
U1 UA741 OP AMP

Description

When the input voltage is 0 the LED glows. The LED stops glowing when the voltage rises to the level determined by R2. Reverse + and - pins to reverse operating mode. To set voltage at which LED goes off, (1) Set 0V at input. (2) Set input voltage at desired level. (3) Adjust R2 to point right after LED goes out.

author: Paul Stilo

Logic Probe by 74LS47

This circuit is a Logic Probe. It indicates the logic state of the node of any TTL logic circuit. To do that, we have to supply the probe with the same power of the circuit that we want to analyse: same Vcc and same GND. ...

Read more and View Circuit

site reciprocates

Binoculars
Shopping and Rating the best binoculars online.

FM Transmitter Bug

This small transmitter uses a hartley type oscillator. Normally the capacitor in the tank circuit would connect at the base of the transistor, but at VHF the base emitter capacitance of the transistor acts as a short circuit, so in effect, it still is. The coil is four turns of 18swg wire wound around a quarter inch former. The aerial tap is about one and a half turns from the supply end. Audio sensitivity is very good when used with an ECM type microphone insert. David's email : radio_david@yahoo.com

Source: http://www.electronics-lab.com/projects/rf/002/index.html

Smart Phone light

The circuit is fully isolated from the phone lines and it draws current only when the phone rings. The circuit provides automatic switching on of a lamp during darkness when the phone is kept in a place such as the bedroom. The lamp can be battery powered to provide light during power failure or load shedding. This avoids delay in attending to a call. The light switches off automatically after a programmable time period and it needs no attention at all. If required, the lamp lighting period can be extended by simply pressing a pushbutton switch (S1). The first part of the circuit functions as a ring detector. When telephone is on-hook, around 48V DC is present across the TIP and RING terminals. The diode in the opto-coupler is ‘off’ during this condition and it draws practically no current from he telephone lines.

Source: http://www.electronic-circuits-diagrams.com/telephonesimages/telephonesckt12.shtml

Soft Musical Telephone Ringer by UM66T

The incoming ring is detected by transistor T1 and components wired around it. In absence of ringing voltage, transistor T1 is cut off while transistor T2 is forward biased as resistor R2 is returned to the positive supply rails. As a result collector of transistor T2 is at near-ground potential and hence IC1 (UM66) is off. Also capacitor C2 is charged to a slightly positive potential. During positive half of the ringing voltage, diode D1 forward biases transistor T1 and rapidly discharges capacitor C2 to near ground potential and cuts off transistor T2 which, in turn, causes IC1 to be forward biased and music signal is applied to base of transistor T3 which drives the speaker. During negative half of the ringing voltage, capacitor C2 cannot charge rapidly via resistor R2 and hence transistor T2 remains cut off during the ringing interval.

Source: http://www.electronics-lab.com/projects/telephone/003/index.html

Time Delay Relay II by IC 4011

When activated by pressing a button, this time delay relay will activate a load after a specified amount of time. This time is adjustable to whatever you want simply by changing the value of a resistor and/or capacitor. ...

Link Time Delay Relay II by IC 4011

Time Delay Relay by 555

A time delay relay is a relay that stays on for a certain amount of time once activated. This time delay relay is made up of a simple adjustable timer circuit which controls the actual relay. ...

Read more and View Circuit