Versatile LED Display Design
Creating a custom LED display for a specific application can be a time-intensive task, especially when designing a decoder tailored to the driver circuit and the display. However, the circuit presented here offers a significant advantage: it allows the same hardware to support various types of display decoding. This versatility is achieved through the utilization of an EPROM. A component most readers are capable of programming or having programmed.
Efficient Translation of Input Code
This circuit efficiently translates a 12-bit input code into appropriate drive signals for a 4-digit readout assembled from 7-segment common-anode LED displays. Each of the four digits necessitates a single byte in the EPROM. By storing these bytes at consecutive addresses, the information can be accessed by applying binary codes 00 through 11 to the two least significant address lines, A0 and A1. As the four displays are multiplexed, manipulating the A0 and A1 lines in this manner enables the retrieval of codes from the EPROM, displaying the corresponding data on the readout. With the remaining address bits of the EPROM available, the circuit is free to process the code to be converted.
Customized Code Translator Using EPROM
In this specific application, an EPROM is programmed to function as a code translator for an RC5 infra-red remote control transmitter. The RC5 receiver, detailed in Reference 1, can be directly connected to the decoder input via connector K1, using a short flat cable. An RC5 code consists of five address bits and a 6-bit key code. In this instance, the two most significant digits are utilized to display the address, while the remaining two represent the key code. The six data bits, five address bits, and the toggle bit are linked to the EPROM address lines. The toggle bit plays a vital role in driving the decimal point on the rightmost digit, indicating when a key is pressed on the remote control unit.
Programming the EPROM Content
The EPROM’s content is generated using the provided Pascal program. It’s important to note that the outputs of the IR receiver operate in an active-low configuration. Consequently, counting must be performed in reverse, ranging from 31 to 0 for addresses and 63 to 0 for data, instead of the usual ascending order (0 to 31 and 0 to 63). This unique counting sequence facilitates the implementation of various decoder configurations, allowing for straightforward adaptation of the EPROM contents as needed. For those seeking convenience, the ready-programmed EPROM to implement the RC5 code readout is readily available from Elektor Electronics.
Parts list
Resistors:
- R1-R8 = 220 Ω
- R9-R12, R14 = 10 kΩ
- R13 = 100 kΩ
- R15, R16 = 6-stage 100 KΩ SIL
Capacitor:
- C1 = 10 nF
- C2 = 220 μF, 16 V
- C3, C4 = 100 nF
Semiconductors:
- T1-T4 = BC557B
Integrated circuits:
- IC1 = ULN2804
- IC2 = 74FICF139
- 1C3 = EPROM1 Type 27128 Ref. 6261*
- IC4 = 4060
Miscellaneous:
- K1 = 20-way straight box header
- LD1—LD4 = HD11050 (Siemens)
- Enclosure, e.g. Heddic Type 222
