Bridge Head

Bridge Head

Pictures!
Jack Antenna Ball!
Jack SeaHawk Ball!

This circuit, Transistor-Head #1. Thanks to Wilf Ritger.

Bridge Head, Wilf Rigter.
This circuit, Bridge-Head #2. Thanks to Wilf Ritger.

The LDR's were hand-picked. Got two packages of them from Radio Shack, looking for at least two pairs of similar parts. Then added wire-wrap pin sockets, to the circuit, so that the LDR's could be plugged in. Currently, the 0.33UF cap is not being used on my B-Head's. I made a long J-hook from "Jumbo Paper Clips", attached it to the motor shaft, and then hung it from my rear-view mirror so it can "see the lights". <grin> (Pix below)

Note: If you choose the kind of LDR that is in a metal transistor type package, rather than the white ceramic type, that is good. If you have the type that is white ceramic, then you do need to cover the back and sides of these LDR's with either heat-shrink or black paint. The reason is that the light goes through the ceramic and affects the LDR, from sides or back. You may want this "feature" depending on what kind of response you want. This modification will increase the sensitivity (maybe). I noticed this because Radio Shack had two of these metal-can type in the last two packs that were purchased. They worked the best of all.

Bridge-Head, by Wilf Rigter, with Phototransistors.

Here is another Wilf Bridge-Head. This one with Radio Shack 276-145A phototransistors.

Hangs on my rear-view mirror, 764 x 1384 JPG

This is how it looks.

Showing the hanger soldered to a DuBro collar, set screwed to the gearmotor output shaft.
Photo Transistors work great in daylight or early dusk. Very active!
CDS cells (LDR's) work best in high contrast areas at night, i.e. dark street with street lights (sodium type).
Having them both in parallel seems to cut the daytime phototransistor response time.
So, for now the LDR's are unplugged.

Gearmotor shown on another page.
Two surplus Lithium 3-volt batteries for 6-volts total.
The "white stuff" is a stiffener compound, usually used to hold electronic parts in place, kinda like hotglue. Under that "white stuff" is the bridge. The sensors are plugged into pin sockets soldered into the circuit. This allows quick change of different types, to test real-life/circuit responses. The bridge is double-sticky-foam-taped to the gearmotor, as are the batteries.

You can see the on/off switch in back.

How it looks if it were hanging.
Shows the CDS cells (LDR's) in parallel with the phototransistor/10K-resistor combo.
Brown & Blue wires are the battery connections.

Today was finished another B-Head circuit. It is free-formed of TO-92 transistors, and mounts on the top of a Nihon Mini-Motor. It is the same diameter as the motor and adds about 1/4" to it's length. Sticking out from the circuit are the IC pin sockets (just like the hanging one) so that various light sensing devices can be tried. All of this fits inside of a hollowed out Jack-In-The-Box (hamburger place) antenna ball, the winter one. The photo-transistors stick out through the ball where Jack's eyes used to be. The collar & scarf on the ball does help hide the motor. For now the batteries are just stuck to the back of the ball, same kind of batteries as above. There is no other opening besides the two eyes and the hole in the bottom. Everything fits through the large hole in the bottom.

Here's that circuitry. Eight transistors on the top of jack's mini motor.

Here's Jack at the football game. He turns and watches the game.
He has solar-cell eyes (water-clear, deep-blue 5mm sized eyes).

Here's a sideview of Jack at the football game.

Paul T. Barton

This page updated: April/04/2002