LOW PASS WITH 10 kHz CUTOFF

Description: The next throttle is a prototype assembled for testing purposes. It represents a modification of the basic transistor throttle. The SPDT switch enables the throttle to deliver either full or half-wave DC output. The value of the 8 µF capacitors is calculated to allow the voltage across the 1000 ohm potentiometer to decay to one-third of the supply voltage before the next cycle begins. At 120 Hz, an 8 µF capacitor is required, while at 60 Hz, a 16 µF capacitor is necessary to achieve this result. Consequently, the peak output voltage of the throttle is three times the lowest output voltage for a specific throttle setting. The waveforms diagram below the schematic provides clarification. If the 8 µF capacitors are omitted, the circuit becomes a complex full-wave DC throttle. The throttle features an automatic current limit of approximately 2 amps and a quasi-regulated output voltage. This throttle performed well with an Atlas locomotive and a starter set commonly seen during the Christmas season. Next is the basic transistor throttle with an unplugged walk-around control added. The direction memory employs an LM339 quad comparator with a delayed action, preventing direction changes if the throttle output exceeds a predetermined voltage. The delayed reverse section, comparator section D, grounds the bases of the transistors whenever the voltage at its PLUS input is higher than the reference voltage at the MINUS input. The PLUS input connects to the throttle control voltage line. When the transistor bases are grounded, they cannot conduct, and any changes at their emitters will not have an effect until the control voltage drops below the preset level. Comparator sections B and C act as a voltage window detector, where both outputs remain high as long as the direction signal voltage is between 4 and 8 volts. If the signal falls below 4 volts or exceeds 8 volts, the corresponding output goes low, resulting in a direction change. If the controller is unplugged, the direction signal will stabilize at 6 volts, maintaining the train's last direction. A voltage comparator information page is available on the website for further assistance on how comparators operate. A variation of the walk-around throttle is presented in the next circuit. By adding extra wires to the control cable, these can be utilized for operating layout accessories. Each additional wire can control two such loads. For example, electromagnetic uncoupling ramps can be activated, train whistles can be blown, or a reverse loop switch can be triggered after the train passes. By employing 4N33 Darlington output optoisolators as low-power relays and incorporating two push buttons or a toggle switch into the handheld controller, a diverse range of external devices can be operated with minimal current draw on the throttle circuit. Unplugged operation remains feasible even with six wires in the control cable, allowing for four auxiliary control outputs. The optoisolator can handle a load current of 20 milliamps; larger load currents necessitate the addition of another transistor. The next drawing provides a more detailed view of the auxiliary outputs. The subsequent circuit incorporates walk-around control into the throttle. A four-conductor, 22 gauge stranded cable enables the operator to move around with the handheld controller while the power section of the throttle remains stationary. A DPDT 24 Volt DC relay and a toggle switch have been added for direction control. The direction switch, speed control potentiometer, and a 10K ohm resistor are mounted in the handheld controller. The initial circuit is a 2 Amp, 0-12 Volt voltage regulator type circuit, utilizing a 10K ohm potentiometer to regulate the output voltage and featuring a light-emitting diode.

The described throttle circuit is designed for model train applications, focusing on versatility and functionality. The SPDT switch allows users to select between full-wave and half-wave DC outputs, facilitating various operational modes. The capacitor selection is critical for maintaining appropriate voltage levels across the potentiometer, ensuring smooth throttle operation at different frequencies. The automatic current limiting feature enhances safety by preventing excessive current draw, which could damage the components or the locomotive.

The incorporation of an LM339 quad comparator for direction control introduces a sophisticated method for managing the throttle's output. The delayed action mechanism ensures that the direction remains stable under certain conditions, enhancing user control and preventing abrupt changes that could disrupt operation. The voltage window detection capability provided by comparator sections B and C allows for precise control over the direction signal, ensuring reliable performance within specified voltage thresholds.

The design’s flexibility is further enhanced by the option to control external accessories through additional wiring. This feature broadens the throttle's application scope beyond just controlling the train, allowing for interactive layout features such as uncoupling mechanisms and sound effects. The use of optoisolators for controlling these accessories ensures that the main throttle circuit is not overloaded, maintaining efficient operation.

The walk-around control feature, facilitated by a four-conductor cable, allows operators to maneuver freely while managing the throttle. This design consideration significantly enhances user experience during operation. The inclusion of a DPDT relay for direction control and the mounting of essential components within the handheld controller streamlines the user interface.

Overall, this throttle circuit exemplifies a well-thought-out design that balances functionality, safety, and user interaction, making it a valuable tool for model train enthusiasts.The next throttle is one that was put together for testing purposes only. As can be seen it is a modification of the basic transistor throttle shown above. The SPDT switch allows the throttle to have a full or half wave DC output. The value of the 8 uF capacitors is calculated to allow the voltage across the 1000 ohm potentiometer to decay to 1/3 of the supply voltage before the next cycle starts. At 120 Hz; 8 uF is needed and at 60 Hz; 16 uF is required to achieve this result. This means that the peak output voltage of the throttle has value that is three times the lowest voltage of the output for a given throttle setting. Please refer to the wave forms diagram below the schematic for clarification. If the 8 uF capacitors are omitted, the circuit becomes an overly-complicated, fullwave DC throttle. The throttle as shown has an automatic current limiting of about 2 amps and a quasi-regulated output voltage.

This throttle gave pretty good results with an Atlas locomotive and one from a starter set of the type that make their appearance at Christmas time. (View) next up is the basic transistor throttle with unplugable walk around control added. The direction memory uses an LM339 quad comparator and has a delayed action so that the direction can not change if the throttle output is above a predetermined voltage.

The delayed reverse section, comparator section D, of the circuit grounds the bases of the transistors whenever the voltage at its PLUS input is higher than the reference voltage at the MINUS input. The PLUS input is connected to the throttle control voltage line. When the transistor bases are grounded they cannot conduct and any changes at their emitters will have no effect until the control voltage again falls below the preset level.

Comparator sections B and C function as a voltage window detector. That is to say the outputs of both section Band C are high as long as the direction signal voltage is between 4 and 8 volts. If the signal goes below 4 volts or above 8 volts the appropriate output will go low and the direction will change accordingly.

If the controller is unplugged the direction signal will go to 6 volts and the train will maintain its last direction. Please refer to the voltage comparator information page on this web site for help on how comparators work.

(View) A variation on the walkaround throttle is in the next circuit. If extra wires are added to the control cable they can be put to use for operating accessories on the layout. For every extra wire 2 such loads can be controlled. Electromagnetic uncoupling ramps could be turned on and off, train whistles could be blown or a reverse loop switch can be thrown after the train has passed.

By using 4N33 Darlington output Optoisolators as low power relays and adding two push buttons or a toggle switch to the hand held controller a wide variety of external devices could be operated with only a small current draw on the throttle circuit itself. Unplugable operation would still be a feasible option even with six wires in the control cable. This would allow four auxiliary control outputs. The optoisolator by itself can only handle a load current of 20 milliamps, larger load currents require adding another transistor.

The next drawing is shows a more detailed view of the auxiliary outputs. (View) In the next circuit walk around control is added to the throttle. A 4 conductor, 22 Gauge stranded cable will allow the operator to move around with the `Hand Held Controller` while the power section of the throttle remains at a fixed location. A DPDT 24 Volt DC relay and a toggle switch has been added for direction control. The direction switch, speed control potentiometer and a 10K ohm resistor are mounted in the Hand Held Controller.

(View) The first circuit is a 2 Amp, 0-12 Volt, voltage regulator type circuit. It uses a 10K ohm potentiometer to control the output voltage and has a light emitting diode t