|
|
Sometimes - as in this case - the stock of electronic
components available may offer some inspiration for a new
project. This one results in a small device, which itself
displays crawling light and is also able to control drivers of
more powerful lamps or even soundgenerators.Since the circuit works differently from what is usually
considered 'running lights', I have chosen another - rather
obvious - name for it. |
The mastercircuit... is made around a hex-buffer. A handful of cheap 100 nF
ceramic capacitors, various resistors and a single transistor
make do for the rest. The construction is suitable for further
experiments and add-ons, so for that end some testpins and a
diode (to give some protection) are employed too.The power consumption is rather modest and batteries (6 -
12 V.) as well as any reasonably stable powersource can be
used.
|
|
Lay-out... is vastly dependent on the size and shape of the actual
components. Here a couple of SIL-resistor-arrays were employed.
They may, however, be replaced by small, conventional resistors
without changing the basic lay-out significantly.In case you decide to try the "crawling light", you may get
some help from the illustrations. Please observe, that a couple
of the connecting wires (not drawn in red!) run on top of
the board -- and that my solution does not have to be the best
one!
|
 |
 |
 |
| The circuit diagram of the master Please notice the minus-/common-ground-rail runs from the
capacitor top, left and down right.Except for the hex buffer-IC (= 4050) there are no special
requirements to the components. |
The very moment power is turned on, the capacitor at the
input of gate 'A' will carry no electrical charge and the input
is 'low'. Consequently all of the gates 'B' to 'F' are low too
and the transistor 'off'. The capacitor at input-A is therefore
charged slowly through the 22k and 1M resistors. After some time
threshold-level for the A-gate is surpassed and its output
switches to 'high', turning on the first Light Emitting Diode
(LED) and starting to charge the capacitor at 'B' a.s.o.a.s.f.
The last of the gates to go high is the F-gate. This turns the
transistor 'on', and starts discharging the capacitor at 'A'. A
new wave of 'going lows' will then proceed from 'A' to 'F'
resulting in the transistor being turned 'off' again and the
cycle repeating itself all over.The spectator will see the LEDs one by one turn on until
they are all lit. Next the first-lit LED will switch off followed
by the rest a.s.o. |
Add-ons: more lightIf the 'crawling light' is to be part of a toy or a display,
higher intensities are needed. For that purpose an external
driver will be useful. I have tried a simple approach like the
one in the diagram. As you will see, I could not stand the
temptation to use the first driver as an inverter for a second
one. The first trio of LEDs does not, in this configuration,
extinguish completely.The drivers (6 of them) run readily on a separate
powersupply and a plain rectifier will suffice. Resistance values
are calculated for 12 V. and 3 yellow or green LEDs. In case
you are bent on red LEDs, just add an extra one, making it to 4
diodes.The drivers, when connected, will prevent the LEDs in the
mastercircuit from lighting up. |
  |
Add-ons: sounds instead of light.Small, adjustable LF-oscillators are readily made around
CMOS-Schmitt-trigger-NAND-gates. These come in packages of 4 (=
4093), so 2 of the kind were required for this purpose.The value of the capacitor 'C' has to be determined
experimentally because the internal parameters of the 4093 affect
the frequency a lot. 1 nF is a good place to start. It is not
adviceable to go lower than 220 pF.Another peculiarity was discovered during my experiments:
apparently there is a smudging effect amongst gates in the same
housing, making two oscillators, running at nearly the same frequency,
'lock' to one another. The problem was partly solved by involving
the vacant two NAND-gates as stand-ins for the troublesome
ones.The 'logic' outputs from the mastercircuit do not match
the controlling input in the oscillators and some modifications
have to be made. You may choose from two possibilities: either
remove (or omit) the LEDs or establish an extra connection
going right to the bufferoutputs. The oscillators are best run from the same powersupply as the mastercircuit. Since the LF-oscillators generate square-waves, the sound
does appear rather harsh and vulgar. Fortunately there is plenty
of it offering ample room for filtering and curveshaping. |
The number of delaying elements does not have to be just 6.
If you like, another (or more) "4050" may be employed between the F-gate
and the transistor base. The propagation of the crawling action is
dependent on the value of the capacitors and will be slower if
bigger capacitors are in use.Two invertergates may replace one buffergate -- worth to
take into consideration, if you have plenty of inverters
but no buffers.
