& Audio Circuit
power supply with audio interface
Joe F. B9-0316
The club standard Tech 22 neon supply is without doubt, the smallest
and lightest option. The primary advantage of the neon supplies
presented here is cost. If all the components were purchased new,
the total cost would not exceed $75. Careful shopping for surplus
easily gets the price under $50
Two versions are presented here: A 12 Volt DC version for mobile
Robots and a 120 Volt AC version for stationary Robots operated
from wall current.
these Instructions in Word (.doc) format
in operation (.avi file)
DISCLAIMER: READ THIS FIRST
Neon power supplies operate at high voltages that are LETHAL.
YOU MUST observe all safety precautions associated with live electrical
circuits. If you are unsure of or unfamiliar with high voltage electrical
practices DO NOT CONSTRUCT THESE CIRCUITS.
The author and distributor(s) of this information accept no liability
for injury or death and / or collateral or property damage arising
from the use, or inability to use this information.
The builder and user accepts all risks.
Use of the information contained herein constitutes your acceptance
of the above disclaimer.
The above in a nutshell: If you attempt to build any of these circuits,
either as shown or modified in any way and you hurt or kill yourself
(or anyone else) and / or burn down the house, your Robot or a grade
school, orphanage, children’s hospital etc,
YOU are solely responsible!
Fig 1 The neon unit in operation
Fig 2 12 Volt DC Version.
Fig 3 Schematic Diagram 12 Volt DC Version
Fig 4 Diagram 120 Volt AC version
Basic theory of operation:
The 12 Volt DC power is converted to 120 Volt AC by an inverter.
The 120 Volts is applied to the ignition coil to step it up to the
high voltage required by the neon.
The solid-state relay is used to switch the 120 Volts from the
inverter to the ignition coil. The solid-state relay is controlled
from an audio source.
The audio is sampled either directly from the speaker terminals
or from a small audio amplifier (100mW or more) that is fed from
the same audio source as the speaker’s amplifier. The second
method is preferable since it allows independent control of the
neon flashing threshold and speaker volume.
The audio transformer steps up the audio sample. The stepped up
audio voltage is AC. The 1N4005 diodes rectify the AC to the DC
required to operate the relay.
The Zener diode limits the applied DC voltage to protect the relay
input. The limiting action allows the relay to be driven harder,
providing cleaner switching of the relay i.e. it’s either
full on or full off.
The capacitor across the relay’s coil filters the DC signal
and sets the syllabic rate (how fast the neon can flash). This filtering
action insures the neon flashes on whole words and not a series
of rapid flashes in time with the audio peaks.
The capacitor in series with the ignition coil limits the AC current
through the coils primary winding to prevent overloading the inverter
or damaging the ignition coil from over current. The capacitor helps
shape the AC current into sharp spikes that are more efficient at
driving the ignition coil.
The capacitor across the ignition coil primary increases the high
voltage generated in the secondary and suppresses the transient
voltages or spikes that are generated by the ignition coil primary.
This helps protect the solid-state relay as well as the inverter
in the DC version and the dimmer in the AC version.
Notes on the 120 Volt AC version:
At first glance, you may wonder why this version includes the dimmer
and incandescent lamp. You might wonder why you couldn’t just
operate the circuit directly from the 120 Volt AC line? The answer
lies with the use of an ignition coil to supply the high voltage.
Unlike a transformer designed for operation from the AC line, ignition
coils are designed to operate on pulses. They depend on the rapid
collapse of the magnetic field that occurs within the coil when
the current is abruptly cut off. (Such as when the points open on
a distributor for those of you old enough to remember cars before
If you study the waveforms of the AC current from various sources
you will see why household current doesn’t work.
The incandescent lamp across the dimmer is for functionality and
not as an indicator of any kind. Lamp dimmers are designed to operate
on purely resistive loads only. This circuit appears too inductive
for the dimmer to function properly.
The lamp “fools” the dimmer into operating as if the
load were resistive. You may find that larger or smaller wattage
lamps may work better in your particular instance.
The dimmer does allow considerable adjustment of brightness but
is primarily adjusted to provide complete stability of illumination.
Good luck, WORK SAFELY! I would be glad to hear from anyone using