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QUESTIONS & ANSWERS
INTERCOM PARTS LIST
PART
SW1
FUSE
T1
D1, D2
C1, C2
U1
C5, C7
SPEAKERS
C3
SW2
RLY1, RLY2
R1
IC1
IC2
C4, C8
C6
R2, R3
R4
R5
R6
R7
DESCRIPTION JAMECO #
SPST POWER SWITCH 317287
5x20 MM CLIP 1712608
115V/12VCT T WO AMPS 29226
1N4004 DIODE, 400V, 1A 35991
3,300 µF, 16V 198898
VOLTAGE REG 5V, 1.5A 924570
0.1 µF, 50V, +80-20% Z5U 15272
4 OHM, 4” DIA 2099614
220 µF, 16V 30496
PUSHBUTTON, MOMENTARY 315660
RELAY, DPDT, 5V COIL 2135291
50K POT, PANEL MOUNT 255434
LM386N AUDIO AMP 24125
LM358AN DUAL OP-AMP 120862
10 µF, 16V, RADIAL 198839
1 µF, 50V, RADIAL 29831
1K, 5%, 1/8W
10K, 5%, 1/8W
4.7K, 5%, 1/8W
10 OHMS, 5%, 1/8W
100K, 5%, 1/8W ■ FIGURE 5.
DC-TO-DC REGULATOR
QI would like to build a well regulated step-down DC-to-DC power regulator built with minimal parts (from Mouser), with an input of 12 VDC 200 mA and an output of 3 VDC 10 mA.
Can you please help create such a schematic?
I have several 12 VDC wall adapters rated at 200 mA
■ FIGURE 4.
(purchased from goldmine-elec.com; #G14801) which
would power-up several kits, each being rated at 3 VDC
@ 10 mA — i.e., one is this five LED random/sequence
flasher whose prerequisite for operating current is
10-16 mA because of the CMOS VLSI single chip-on-board contained in the circuit (any higher current would
destroy the chip-on-board).
— Michael Williams
ASince efficiency is not a consideration, a shunt regulator is the simplest solution. Take a look at Figure 6. The LM431A is rated at 36 volts and 100 mA max, and the reference voltage is 2.5V
±2%. The theoretical value for R2 is 400 ohms, so the 20
ohm pot allows you to get the
right value and also trim out the
tolerance. The load current is
limited to 15 mA by R1; if the
load tries to draw more current,
the voltage will reduce.
HIGH VOLTAGE
GENERATOR
QMy project is a simple one. I only want to make sparks! Either a mesmerizing toy to
watch or a Jacob’s ladder. I
have this circuit I built to drive
■ FIGURE 6.
June 2013 27