Background
The decoder used is an SN74LS138 3-to-8 decoder. The package is contained in a standalone IC package. The decoder is used to select which row of LEDs is being powered.
The decoder used is an SN74LS138 3-to-8 decoder. The package is contained in a standalone IC package. The decoder is used to select which row of LEDs is being powered.
Implementation
The decoder is implemented between the HCS12 and the transistor circuit and is used to select a single row of LEDs out of the 6. Its output is ran into an inverter to be implemented with the transistor circuit.
The decoder is implemented between the HCS12 and the transistor circuit and is used to select a single row of LEDs out of the 6. Its output is ran into an inverter to be implemented with the transistor circuit.
Test Procedure
We built a test circuit on a breadboard consisting of 8 LEDs and a 4 input digital switch. We connected an LED to each of the decoder’s outputs and wired 3 inputs from the digital switch to the 3 inputs on the decoder.
Test Results
We shifted 8 different bit patterns into the decoder and watched as each of the 8 LEDs on the board lit up one at a time. Successful completion of this test verified the decoder was working properly.
We built a test circuit on a breadboard consisting of 8 LEDs and a 4 input digital switch. We connected an LED to each of the decoder’s outputs and wired 3 inputs from the digital switch to the 3 inputs on the decoder.
Test Results
We shifted 8 different bit patterns into the decoder and watched as each of the 8 LEDs on the board lit up one at a time. Successful completion of this test verified the decoder was working properly.