Lens lamp not strong enough

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Lens lamp not strong enough

Beitragvon MisutaaRobotto » 09 Aug 2019, 20:34

I had this problem in another fischertechnik set before, but the lens lamp is by far not strong enough to bridge the distance to the phototransistor on the other end. This seems to be a structural issue. I did some tests with values measured, and if the distance becomes more than 4-5 cm, the phototransistor doesn't measure anything anymore.

1. I have verified again and again that I'm using the lens lamp, not the LED lamps
2. This happened in another set too (bought years ago), with different lens lamps and different phototransistors

Can anyone confirm this? Any tips? The models in the Robotics set need to bridge distances of 10 cm if not more, and I seem to be very far away from that.
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Registriert: 09 Aug 2019, 20:31

Re: Lens lamp not strong enough

Beitragvon fishfriend » 09 Aug 2019, 21:47

The LDR make no differents between sunlights or lamps.
There are two ways:
1. Take a tube on the LDR. There is a (ft part) black cap - and - a red tube.
2. You test the LDR only when the lamp is on. So if you frequently turn the lamp on and off, you can detect it.
Best regards
Holger Howey
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Registriert: 26 Nov 2010, 12:45

Re: Lens lamp not strong enough

Beitragvon PHabermehl » 09 Aug 2019, 23:17


what type of input do you use? You have to configure the input as "digital", and RoboPro will just read 1 or 0. The phototransistor is not meant to read out analog values, i.e. voltage or resistance. It's just conductive or non-conductive depending on the light. And it works even for wider distances than 10 cm.

Kind regards,
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Re: Lens lamp not strong enough

Beitragvon steffalk » 10 Aug 2019, 10:35


also, if the distance is large, you may need to adjust the position of the lamp so that it really targets the LDR. In the 1970s, the BS15 with round red nops were used to adjust the lamp in both directions (vertical to its beam).

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Re: Lens lamp not strong enough

Beitragvon vleeuwen » 10 Aug 2019, 12:15

You can do some test/experiment yourself.
Connect the resistor or phototransistor to two Inputs, one digital and one analogue. The impedances of the inputs are high enough to do so.
Make in RoboPro a small program that shows also the analogue value on a meter (RoboPro scoop) and that you are able to see what's happening when the light is on or off.
This can also help you to adjust the position of the lens lamp. (or small angle LED).
With this test you can also see the influence of the back ground light. Maybe you will need the cover the back ground light with a piece of paper.

It is very often very useful to create some tests for a sensor yourself. This help you to understand what is happening and how the control system is working.
This is also an objective for fischertechnik. Try to understand how it 's working. This improve the skills to create or adjust models.
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