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. ...

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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