Wiring & diagram Info: model

Sunday, November 9, 2014

Model Railway Short Circuit Beeper

Short circuits in the tracks, points or wiring are almost inevitable when building or operating a model railway. Although transformers for model systems must be protected against short circuits by built-in bimetallic switches, the response time of such switches is so long that is not possible to immediately localise a short that occurs while the trains are running, for example. Furthermore, bimetallic protection switches do not always work properly when the voltage applied to the track circuit is relatively low. The rapid-acting acoustic short-circuit detector described here eliminates these problems. However, it requires its own power source, which is implemented here in the form of a GoldCap storage capacitor with a capacity of 0.1 to 1 F. A commonly available reed switch (filled with an inert gas) is used for the current sensor, but in this case it is actuated by a solenoid instead of a permanent magnet.

An adequate coil is provided by several turns of 0.8–1 mm enamelled copper wire wound around a drill bit or yarn spool and then slipped over the glass tube of the reed switch. This technique generates only a negligible voltage drop. The actuation sensitivity of the switch (expressed in ampère-turns or A-t)) determines the number of turns required for the coil. For instance, if you select a type rated at 20–40 A-t and assume a maximum allowable operating current of 6 A, seven turns (40 ÷ 6 = 6.67) will be sufficient. As a rule, the optimum number of windings must be determined empirically, due to a lack of specification data. As you can see from the circuit diagram, the short-circuit detector is equally suitable for AC and DC railways. With Märklin transformers (HO and I), the track and lighting circuits can be sensed together, since both circuits are powered from a single secondary winding.

Coil L1 is located in the common ground lead (‘O’ terminal), so the piezoelectric buzzer will sound if a short circuit is present in either of the two circuits. The (positive) trigger voltage is taken from the lighting circuit (L) via D1 and series resistor R1. Even though the current flowing through winding L1 is an AC or pulsating DC current, which causes the contact reeds to vibrate in synchronisation with the mains frequency, the buzzer will be activated because a brief positive pulse is all that is required to trigger thyristor Th1. The thyristor takes its anode voltage from the GoldCap storage capacitor (C2), which is charged via C2 and R2.

The alarm can be manually switched off using switch S1, since although the thyristor will return to the blocking state after C2 has been discharged if a short circuit is present the lighting circuit, this will not happen if there is a short circuit in the track circuit. C1 eliminates any noise pulses that may be generated. As a continuous tone does not attract as much attention as an intermittent beep, an intermittent piezoelectric generator is preferable. As almost no current flows during the intervals between beeps and the hold current through the thyristor must be kept above 3 mA, a resistor with a value of 1.5–1.8 kΩ is connected in parallel with the buzzer. This may also be necessary with certain types of continuous-tone buzzers if the operating current is less than 3 mA. The Zener diode must limit the operating voltage to 5.1 V, since the rated voltage of the GoldCap capacitor is 5.5 V.

Author: R. Edlinger - Copyright: Elektor Electronics

Lighting Up Model Aircraft

This circuit provides aircraft modellers with extremely realistic beacon and marker lights at minimum outlay. The project ’s Strobe out-put (A) provides four brief pulses repeated periodically for the wing (white strobe) lights. In addition the Beacon output (B) gives a double pulse to drive a red LED for indicating the aircraft’s active operational status. On the proto-type this is usually a red rotating beacon known as an Anti-Collision Light (ACL). The circuit is equally useful for road vehicle modellers, who can use it to flash headlights and blue emergency lights.

Lighting Up Model Aircraft Circuit diagram :

Lighting Up Model Aircraft Circuit Diagram

All signals are generated by a 4060 14-stage binary counter and some minimal output selection logic. Cycle time is determined by the way the internal oscillator is con-figured (resistor and capacitor on pins 9/10) and can be varied within quite broad limits. High-efficiency LEDs are your first choice for the indicators connected to the Bea-con and Strobe outputs (remember to fit series resistors appropriate to the operating voltage Ub and the current specified for the LED used).

The sample circuit is for operating voltages between 5 and 12 V. Cur- rent flow through the two BS170 FET devices must not exceed 500 mA.

Voltage Tester for Model Batteries

With a suitable load, the terminal voltage of a NiCd or lithium-ion battery is proportional to the amount of stored energy. This relationship, which is linear over a wide range, can be used to build a simple battery capacity meter.

Voltage Tester for Model Batteries Circuit Image

This model battery tester has two functions: it provides a load for the battery, and at the same time it measures the terminal voltage. In addition, both functions can be switched on or off via a model remote-control receiver, to avoid draining the battery when it is not necessary to make a measurement. The load network, which consists of a BC517 Darlington transistor (T2) and load resistor R11 (15 Ω /5 W), is readily evident. When the load is active, the base of T1 lies practically at ground level. Consequently, T1 conducts and allows one of the LEDs to be illuminated.

Circuit Diagram :
Voltage Tester for Model Batteries-Circuit Diagram

Voltage Tester for Model Batteries Circuit Diagram

The thoroughly familiar voltmeter schema, which is based on the LM3914 LED driver, determines which LED is lit. The values of R6 and R7 depend on the type and number of cells in the battery. The objective here is not to measure the entire voltage range from 0 V, but rather to display the portion of the range between the fully charged voltage and the fully discharged voltage. Since a total of ten LEDs are used, the display is very precise. For a NiCd battery with four cells, the scale runs from 4.8 V to 5.5 V when R6 = R7 = 2 kΩ. The measurement scale for a lithium-ion battery with two cells ranges from 7.2 V to 8.0 V if R6 = 2 kΩ and R7 = 1 kΩ.

For remote-control operation, both jumpers should be placed in the upper position (between pin 1 and the middle pin). In this configuration, either a positive or negative signal edge will start the measurement process. A positive edge triggers IC1a, whose output goes High and triggers IC1b. A negative edge has no effect on IC1a, but it triggers IC1b directly. In any case, the load will be activated for the duration of the pulse from monostable IC1b. Use P12 to set the pulse width of IC1a to an adequate value, taking care that it is shorter than the pulse width of IC1b.

If the voltage tester is fitted into a remote-controlled model, you can replace the jumpers with simple wire bridges. However, if you want to use it for other purposes, such as measuring the amount of charge left in a video camera battery, it is recommended to connect double-throw push-button switches in place of JP1 and JP2. The normally closed contact corresponds to the upper jumper position,while the normally open contact corresponds to the lower position.

Parts :

Resistors:
R1,R2 = 47kΩ
R3 = 100kΩ
R4 = 500kΩ
R5 = 1kΩ
R6,R7 = see text (1% resistors!)
R8 = 1kΩ5
R9 = 1kΩ2
R10 = 330Ω
R11 = 15Ω 5W
R12 = 15kΩ
P1 = 100kΩ preset
Capacitors:
C1 = 10nF
C2 = 100nF
Semiconductors:
D1-D10 = LED, red, high effi-ciency
T1 = BC557
T2 = BC517
IC1 = 74HC123
IC2 = LM3914AN
Miscellaneous:
PC1,PC2,PC3 = solder pin
JP1,JP2 = jumper or pushbutton

PCB Layout :
B. PCB Laout

Voltage Tester for Model Batteries PCB Layout

Wiring & diagram Info

Sunday, November 9, 2014

Model Railway Short Circuit Beeper

Friday, October 17, 2014

Lighting Up Model Aircraft

Lighting Up Model Aircraft Circuit diagram :

Friday, August 8, 2014

Voltage Tester for Model Batteries