duty cycle range over which a par-
ticular valve is effective, and the best
frequency at which to pulse it, can often
be found only through testing the valve.
This set-up can easily achieve that.
Another application of a variable
duty cycle / variable frequency driv-
er is when testing car fuel injectors.
When injectors are being fl ow tested,
they need to be pulsed at frequencies
that replicate how they are run in an
engine (eg, 8-50Hz) and at different
duty cycles, eg, from 3-80%. Again,
these control modules can easily
achieve that.
You can also use the system as a
speed control for an electric motor- run from a regulated supply, you
should be able to quite precisely and
higher current loads at lower duty cy-
cles – eg, 10A at 50% duty cycle.)
A maximum PWM frequency of
20kHz is specifi ed. Any voltage from
3-20V can be used as the PWM signal,
and the output will work over a 3.7-27V
range. That makes this module a good
match with the frequency generator –
eg, run them off the same 4-20V supply.
Uses
The combination of the driver board
and the variable frequency/duty cycle
module allows you to do lots of things!
One use is testing 12V PWM sole-
noids, used as fl ow control valves. In
addition to being switched on or off,
solenoid valves can be triggered with
a variable PWM signal, resulting in a
variable fl ow capability. However, the
Using this MOSFET module allows the
frequency generator to drive higher
current loads – up to 5A continuous, and
proportionally more at lower duty cycles.
As with the frequency generator, the
connections are clearly labelled. The
Gnd and PWM terminals connect to the
respective terminals on the frequency
generator. Power and ground connect to
the (DC+) and (DC–) terminals, and the
load is connected to the Out terminals.repeatedly dial-up specifi c speeds of
devices like engravers, fans... whatev-
er you need to drive. The system can
also work as a low-voltage DC light
dimmer – set a suitably high frequen-
cy and then control the brightness just
by altering the duty cycle.
Finally, the system can be used to
pulse a light or buzzer. The versatility
of the settings means you can specify
whatever frequency and duty cycle you
want. For example, to save power, use
a higher frequency (eg, 5Hz) and a low-
er duty cycle (eg, 10%). For maximum
attention, use a lower frequency (eg,
1Hz) and a longer duty cycle (eg, 50%).
And I am sure that I’ve only just
scratched the surface of possible uses!Next month
In June, a slight change from my usual
Electronic Building Blocks column. I’ll
be covering the use of thermal imaging
cameras and asking are they worth it
in hobby electronics? One thing I can
vouch for – it took great images of Vic-
tor, our pet sheep, on a cold morning!ELECTRONI CS
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