Readout Circuit

The circuit uses a serial-in-parallel out shift register, 74HC595 for receiving serial data from uController board. See example of U5 in the schematic, SER is for data input, SRCLK is shift clock and RCLK is Latch clock. Each data bit is shifted into the register on rising edge of the shift clock. When all data bits are shifted into the 8-bit register, the rising edge of RCLK will clock the data to be latched at each output bit, i.e. QA - QH...

This sign I designed uses no microprocessor. It has an eprom and multiple counters. As in most electric signs, the LEDs are matrixed, and strobed very quickly to make it possible for all 70 LEDs to appear lit. This sign is strobed horizontally, unlike most large signs which are strobed vertically. I did it this way because electrically it was simpler. The eprom has 8 outputs, of which I used 7 of them to drive the 7 horizontal rows. The eprom outputs are not strong, so they are buffered. The 10 vertical columns are activated in sequence, giving a 1/10 duty cycle...

The circuit in Figure 1 uses a PIC16C55 µP to read 10-bit binary data and directly display the data in decimal format on three common-cathode LED displays. If value of the data exceeds 999, the displays show three hyphens (---) to represent overflow. The PIC16C55 has high drive capability. Each output pin can source 20 mA and sink 25 mA; the outputs can thus directly drive the LED display...