Application of Zener diodes for voltage regulation.
Application of the NE555 timer IC in the astable mode of operation.
This Manual EPROM Programmer is a low-cost circuit that can manually program binary data into 2716 and 2732 EPROMs. The circuit provides two 8-way DIP switches- one for the address of the program and the other for the data of the program.
No. of ICs used: 2
The Manual EPROM Programmer circuit uses the NE555 timer IC (denoted as IC2) wired as a monostable. When the push-to-on switch (S1) is pressed, IC2 generates a 50ms pulse, which is given to the program pin (Pin18) of the ZIF SOCKET through switch S2. EPROM is inserted into the ZIF SOCKET for programming. A red LED (LED1) glows to indicate the application of the programming pulse to the EPROM. Before applying the programming pulse to the EPROM, select the programming voltage (25V, 21V or 12.5V, as specified by the manufacturer) applied to Pin21 of the ZIF SOCKET by using jumper J1. The programming voltage required for an EPROM is sometimes written on its body. The address and data for the EPROM (ZIF SOCKET) are set by using the two DIP switches (SW1 and SW2), respectively, whose pins are initially pulled high via 10-kilo-ohm resistors.
The AC mains is stepped down by transformer X1 to deliver 30V, 250 mA from the secondary. The secondary output is rectified by diode D1 and filtered by capacitor C1. The programming voltages of 25V, 21V and 12.5V are generated with the help of zener diodes ZD1, ZD2 and ZD3. IC1 is used to provide +5V regulated supply to the circuit.
To begin with, first read the programming voltage written on the EPROM. Now insert the EPROM chip into the 24-pin ZIF socket and slide switch S2 as per EPROM. Then connect the power supply to provide regulated 5V DC to the circuit. Select the programming voltage using jumper J1 and set the programming address and data value using switches SW1 and SW2, respectively. After providing the required programming voltage, press switch S1 to program the data at the desired address. Repeat this procedure for the next address and corresponding data.
