# Neon Lamp Tricks!

## Neon Lamp Multivibrator

This is an oscillator circuit using two neon lamps, two resistors, and one capacitor.

```
+-----------------+----->
|                 |
>                 >
> R               > R
>                 >
|        C        |
+-------| |-------+
|                 |
O lamp            O lamp
|                 |
+-----------------+----->

```
The neon lamps blink alternately. The frequency varies, but is generally near 1/(R*C) to up to a few times this. The frequency is higher as supply voltage increases, and is lower if the starting and sustaining voltages of the neon lamps are more different from each other.

This oscillator works at any frequency up to several kilohertz. The neon lamps should be similar. The resistors should be high enough to limit the current through one neon lamp to an appropriate value, considering that the current flows through both resistors but only through one neon lamp at a time. For NE-2H lamps with a 160-170 volt DC supply, the resistors should be at least 68K. For NE-2 lamps with a 160-170 volt DC supply, the resistors should be at least 330K, preferably at least 470K.

DC power may be applied to this circuit in either polarity.

One nice trick to do with this circuit is to use a piezoelectric tweeter as the capacitor. Most piezoelectric tweeters have a capacitance of about .15 uF. This makes an audible buzzer out of this circuit. Adding a small capacitor in series with the piezo tweeter makes the frequency higher. Such a capacitor may be around .001 to .01 uF. With higher audio oscillation frequencies, the piezo tweeter makes a reasonably loud tone with well-filtered DC. With less well filtered DC, the tone becomes buzzy. With unfiltered DC or with AC (This works with higher audio oscillation frequencies) the sound is an annoying screechy buzz.

Forwarded to this site by Sam Goldwasser (sam@stdavids.picker.com):

```   ****************  Interesting Sequential Neon Flasher  ****************

This is a sort of brain teaser since it certainly isn't intuitively obvious
how this circuit works (if it works at all).  It may be instructive to start
with the degenerate case of 2 resistors, 2 neon lamps, and a single capacitor.
What happens with that configuration?

(From: Steve Roberts (osteven@akrobiz.com)).

+200V o----+-----+-----+-----+-----+
|     |     |     |     |
/     /     /     /     /
\ R1  \ R2  \ R3  \ R4  \ R5    R1-R5: 2.7M
/     /     /     /     /
\     \     \     \     \
|     |     |     |     |
+-o A +-o B +-o C +-o D +-o E
|     |     |     |     |
| IL1 | IL2 | IL3 | IL4 | IL5   IL1-IL5: NE2
+-+   +-+   +-+   +-+   +-+
|o|   |o|   |o|   |o|   |o|
+-+   +-+   +-+   +-+   +-+
|     |     |     |     |
Gnd o----+-----+-----+-----+-----+

Connect a .22 uF, 200 V capacitor between each of the following pairs of
points: A to C, A to D, B to D, B to E, C to E.

Neons will flash in sequence ABCDE if fed off DC.  Momentarily removing the DC
will cause them to flash EDCBA.

>From an ancient Radio Shack "Pbox" kit - the first kit I ever built!
```

Written by Don Klipstein.