This programmable sequencer's circuit schematic could be used for a variety of time purposes. An audible tone is generated prior to the start of each interval, and the interval number is displayed on a seven-segment LED display. The buzzer rings again just before the end of that inerval. IC1 is a 2240 timer/counter device capable of clocking up to 256 periods, the lengths of which are regulated by resistor R1 and capacitor C1. The 2240's RESET and TRIGGER pins (10 and 11) are connected by a push switch S1.The timer is used to power IC2, a memory chip. The timer/counter uses the first 8 addressed bits to step through the 256 steps allowed for each program.
The remaining 6 bits are chosen by an external switch network S2 to S7, which supports up to 26 programs, each with 256 steps. The 27C64 has eight outputs, which were sufficient for a single-digit LED display and a piezo buzzer. The ULN2803A is a Darlington transistor array with a high voltage and high current. The circuit is made up of eight npn Darlington pairs with high-voltage outputs and common-cathode clamp diodes for switching inductive loads. Each Darlington pair has a collector-current rating of 500 mA. For greater current capability, the Darlington pairs can be connected in parallel.
Relay drivers, hammer drivers, light drivers, display drivers (LED and gas discharge), line drivers, and logic buffers are examples of applications. Each Darlington pair in the ULN2803A features a 2.7-k series base resistor for direct operation with TTL or 5-V CMOS devices.
No comments:
Post a Comment