Traffic Light Control Circuit

This page features a circuit that has twenty open collector outputs that turn on one at a time in a continuous sequential manner. The circuit utilizes the 74LSxx family of TTL integrated logic devices. The circuits are designed to drive light-emitting diodes or low current, low voltage incandescent lights but can also drive other loads of up to 80 milliamps. As logic circuits go, the 20 Step circuit is fairly simple, but due to the high-speed nature of the TTL Logic devices used, care must be taken when wiring these circuits. Simply put; the neater the wiring, the better. If there is an intention to use these circuits, it is advisable to find and read at least the first two pages of the manufacturer's data sheets for the integrated circuits. Using Google, search for "74ls(part number)" in the first box and "PDF" in the second box on the advanced search page. The circuit does not drive the 74LS145s directly but uses a 74LS107 JK Flip-Flop and four 74LS32 dual input OR gates to control the inputs to the two 74LS145 output drivers. The 74LS107 and 74LS32 are used to create disallowed states in the output drivers alternately. The disallowed states prevent any of the ten outputs on that particular device from being turned ON while the other 74LS145 is counting to ten. This produces a system where only one of the 74LS145s is able to produce a LOW output state at a time. In essence, the circuit counts to 10 twice in succession rather than counting to 20 in a single cycle. This may seem like an unusual method, but it allows the circuit to make economical use of the open collector outputs of the 74LS145s decoder/drivers rather than using output buffer ICs driven by 74LS138 logic devices. The TTL logic devices in the circuit require a regulated 5 volt supply and draw approximately 60 milliamps. The outputs of the 74LS145s can be supplied from up to 15 Volts with a maximum current of 80 milliamps. The following is a parts list for use with the 20 Output Sequencing Circuit. Mouser Electronics part numbers are shown, but the parts may be available from other sources as well. Suppliers that handle NTE components should be able to get the ICs.

The described circuit is a sequential output driver featuring twenty open collector outputs capable of activating one output at a time in a continuous sequence. Leveraging the 74LSxx series of TTL logic devices, this circuit is particularly suited for controlling light-emitting diodes (LEDs) and low current incandescent lamps, with a maximum load capacity of 80 milliamps. The design prioritizes simplicity while acknowledging the rapid switching characteristics inherent to TTL logic, necessitating careful wiring practices to minimize interference and ensure reliable operation.

The circuit architecture incorporates a 74LS107 JK flip-flop, which plays a pivotal role in managing the sequencing of outputs. This flip-flop, combined with four 74LS32 dual-input OR gates, regulates the inputs to two 74LS145 output drivers. The strategic use of these components facilitates the creation of disallowed states, effectively preventing simultaneous activation of outputs on a given 74LS145 while the other is engaged in its counting cycle. This design choice allows the circuit to operate in a manner that counts to ten twice, rather than a single count to twenty, optimizing the utilization of the open collector outputs.

Power requirements for the TTL logic devices are specified at a regulated 5 volts, with a current draw of approximately 60 milliamps. The 74LS145 output drivers can handle supply voltages up to 15 volts, maintaining a maximum output current of 80 milliamps. This flexibility in voltage and current handling enhances the circuit's versatility in various applications.

For implementation, a detailed parts list is available, primarily featuring components from Mouser Electronics, although alternative suppliers may also stock the necessary integrated circuits. It is recommended that individuals interested in constructing this circuit familiarize themselves with the manufacturer's data sheets to ensure proper understanding and application of each component.This page features a circuit that has twenty open collector outputs that turn on one at a time in a continuous sequential manner. The circuit make use of the 74LSxx family of TTL integrated logic devices. The circuits are designed to drive light emitting diodes or low current, low voltage incandescent lights but can also drive other loads of up to

80 milliamps. As logic circuits go, the 20 Step circuit is fairly simple but due to the high speed nature of the TTL Logic devices used, care must be taken when wiring these circuits. Simply put; The neater the wiring the better. If you would like to make use of these circuits, please take the time to find and read at least the first 2 pages of the manufactures data sheets for the integrated circuits.

Using Google, search for "74ls(part number)" in the first box and "PDF" in the second box on the advanced search page. The circuit does not drive the 74LS145`s directly but uses a 74LS107 JK Flip-Flop and four 74LS32 dual input OR gates to control to the inputs to the two 74LS145 output drivers.

The 74LS107 and 74LS32 are used to create disallowed states in the output drivers alternately. The disallowed states prevent any of the ten outputs on that particular device from being turned ON while the other 74LS145 is in counting to ten. This produces a system where only one of the 74LS145`s is able to produce a LOW output state at a time.

In essence the circuit counts to 10 twice in succession rather than counting to 20 in a single cycle. This may seem like an unusual method but it allows the circuit to make economical use of the open collector outputs of the 74LS145s decoder/drivers rather using output buffer ICs driven by 74LS138 logic devices.

The TTL logic devices in the circuit require a regulated 5 volt supply and draw approximately 60 miliamps. The outputs of the 74LS145`s can be supplied from up to 15 Volts with a maximum current of 80 milliamps.

The following is a parts list for use with the 20 Output Sequencing Circuit. Mouser Electronics part numbers are shown but the parts may be available from other sources as well. Suppliers that handle `NTE` components should be able to get the ICs. 🔗 External reference