one minute but still be able to do fi ner
adjustments with brief switch presses.
Having reached your target fre-
quency, insert JP1. Then press S2 to set
the upper threshold frequency. Then
remove JP1. Then press S1 to reduce
the frequency to the lower threshold.
Then re-insert JP1 and press S1 to set
the lower frequency threshold.
Note the two-step process to set each
frequency. In other words,with JP1 out,
use S2 and S1 to adjust the frequency to
the vehicle battery won’t go fl at after
long periods of being parked.
The easiest way to connect the GND
terminal in a vehicle is to wire it to the
chassis using a crimped eyelet secured
to a convenient screw terminal.
You may need to drill a separate
hole in the chassis for this connection,
or utilise an existing earth connection.
Wire CON2 to a suitable sensor. This
can be the speedometer sensor, an ECU
tachometer output, an injector or cam-
shaft position sensor and so on. If you
haven’t already set the unit up, do so as
described above above.
The relay contacts are labelled Nor-
mally Open (NO), Normally Closed (NC)
and Common (COM).
To switch power to a load, wire one
of its supply lines in series between
either the COM and NO terminals (so
that it’s only powered when the relay
is energised) or COM and NC terminals
(so that it’s switched off when the relay
is energised).
Note that the relay contact current
rating is 5A for the Jaycar relay and 8A
for the Altronics relay (see parts list).
If a higher current is required, you
can switch 12V DC to the coil of a larger
relay using RLY1.the wanted value, insert JP1 and press
S2 to set the upper threshold.
Then remove JP1, use S1 and S2 to
obtain the lower threshold frequency,
insert JP1 again and press S1.
Alternatively, if you just want to set
the upper threshold frequency with
S2 and have the hysteresis setting
made for the lower threshold as set by
trimpot (VR2), then you must have a
link fi tted to JP2 before you start the
procedure. Similarly, you can set the
lower threshold with S1 and have the
upper threshold set by the hysteresis
percentage value as set by VR2.
Now turning off the power takes
the micro out of the mode whereby it
produces an output frequency at TP3.
It then reverts to normal operation,
monitoring the input frequency instead.
Then fi t a link to JP1 if you want the
relay to switch on as the frequency
falls below the threshold set by S1
(and turns off when the frequency rises
above that set by S2).
No link is required at JP1 if you want
the relay to switch on as the frequency
rises above the threshold set by S2 (and
turns off when the frequency drops
below that set by S1).
If you want to confi gure the unit with
a switching delay (as described earlier)
you need to adjust trimpot VR2. You can
set the delay anywhere between zero
and half a second. If you don’t want a
delay set VR2 fully anti-clockwise.Installation
Connect the 10-16V DC power source
between the +12V and GND inputs at
CON1. For automotive installations,
automotive-rated wire should be used
and the +12V terminal needs to connect
to the switched side of the ignition.
That way, the unit only operates
when the ignition is switched on and1 double-sided PCB coded 05104181,
102 x 58.5mm
1 DPDT 12V DC coil relay (RLY1)
[Jaycar SY-4052 {5A},
Altronics S 4270A {8A}]
2 2-way screw terminals with 5.08mm
pin spacing(CON1,CON2)
2 3-way screw terminals with 5.08mm
pin spacing (CON3)
2 2-way pin headers with shorting
blocks (JP1,JP2)
1 18-pin DIL IC socket (for IC1)
1 20MHz crystal (X1)
2 SPST PCB-mount tactile pushbutton
switches (S1,S2)
[Jaycar SP0600, Altronics S 1120]
2 PC stakes (TP GND,TP3)
Semiconductors
1 PIC16F88-I/P microcontroller
programmed with 0510418A.HEX
(IC1)
1 LP2950ACZ-5.0 low dropout
regulator (REG1)
1 BC547 100mA NPN transistor (Q1)
1 BC337 500mA NPN transistor (Q2)
1 16V 1W zener diode (1N4745) (ZD1)
2 1N4004 1A diodes (D1,D3)
1 1N4148 signal diode (D2)
7 3mm LEDs (LED1-LED7)Capacitors
1 100μ F 25V PC electrolytic
2 10μ F 16V PC electrolytic
1 10μ F non-polarised (NP) PC
electrolytic
4 100nF 63V/100V MKT polyester
1 1nF 63V/100V MKT polyester
1 470pF ceramic
2 27pF NP0/C0G ceramic
Resistors and Potentiometers
(all 1%, 0.25W)
1 1MΩ 1 100kΩ 4 10kΩ
6 3.3kΩ 1 1kΩ 1 47Ω
1 10kΩ vertical multi-turn trimpot,
3296W style (VR1)
1 10kΩ mini horizontal trimpot, 3386F
style (VR2)Parts list – Deluxe
Frequency SwitchUsing a tacho signal
Imagine you are using the engine tacho
signal to switch the relay if a certain
engine RPM is exceeded – for example,
6000 RPM.
If you have a 4-cylinder, 4-stroke
engine, 6000 RPM = 100 revolutions per
second. Since this type of engine fi res
two cylinders per crankshaft rotation,
then the threshold should be set to
200Hz [100 x 2].The Deluxe Frequency SwitchPCB is designed to fi t into a UB3 Jiffy box, as
shown here – but it could also be ‘built in’ to equipment it is controlling. You
may also be able to source the 10-16V DC from that equipment – as long as it
isn’t turned off by the frequency switch!Reproduced by arrangement with
SILICON CHIP magazine 2019.
http://www.siliconchip.com.au