Hi,

I do have a pair of older Imhoff photocells (sender and reciever).
The reciever is connected to +12V and 0V for power and on signal, there are +12V if the gate is open (or closed? - if someone is running through the gate).

I need to connect this cells to my FinishLynx system - but the FinishLynx box awaits the connection between the to connectors to be closed.

So I need to make a closed connection out of my +12V on signal.

1st Method: Using a simple electromagnetic relay.
But this may be not fast enough for timing purpose.

2nd Method: Using a transistor as a switch.
But I have no idea, how to design this circuit.
What current and which power is between the connectors on the Lynx box. What type of trnsistor can I use? what resistor between signal and base?

Could anyone help me out?

Thanks

Dirk

Hi,
to make a standard connection -open collector -You need a standard low power NPN transistor(like BC547, BC337), resistor to reduce base current -10 kiloohms, and Zener diode 2.7V or 3.3V to prevent transistor from "rest voltage" on fotocell output, in "low" state slighly higher than 0V.
Everything low power, it`s enough.

Connect serially, from photocell output -resistor,cathode of Zener diode, Zener anode to base of transistor. Ground power(0V) of cell to transistor emitter and standard banana black conector.
Then transistor collector to green banana conector and -voila.

In place of zener diode You can use diode 1n4148(or two serially) but in opposite direction, from cell/resistor-to anode, kathode to transistor base.

Without thiese diodes everything maby would work O.K. but only, if there is not more then 400 milivolts on photocell output in low state.

Wish You only like-this problems!

Jaroslaw
Gro-Timing
Poland

Hi Jaroslaw,

you mean like this:


I do not have a green connector on the Lynx box, but 3 pairs in red and black.
Topmosts is for power output, the to others are cell A and cell B
I asume, that all the black connectors are connected within the box.

So I connect the transistors collector to the red connector of either cell A or cell B...

I will try that...

Thanks

Dirk

Hi Dirk,
the schematic is O.K. and according to Lynx documentation (I got no Lynx) Yours connections will work, as other standard photocell.

Interesting, that they use in Lynx-Connnction Box the same color for different functions.

Jaroslaw Grondal
Poland
www.gro-timing.com

Today, I got the chance to try this out - and it worked...

Thanks

dirk