tobiasreber@freesurf.ch wrote: > Hi everyone, > > I am in urgent need of a flow chart for a light sensor that will work with > the i_Cube by Infusion Systems, like the one they sell themselves (http://infusionsystems.com/catalog/product_info.php/cPath/24/products_id/51). > It just consists of a photo cell an a resistor on a small board, but I don't > know whether they're parallel or serially connected. the three cables are > the power, signal an ground connections.

+5 V ()-------- | 1k Ohm | OUT ()-------- | LDR | GND ()--------

LDR is the light sensor, the 1k resistor forms a voltage divider with the resistance of the LDR. Depending on the resistance of the LDR you have to experiment a bit to find a suitable value for the 1k, it's just a guess.

Olaf

Es war der 29.12.2006 12:57 Uhr, als tobiasreber@freesurf.ch nicht widerstehen konnte, folgende Gedanken dem Netz anzuvertrauen:

> Hi everyone, > > I am in urgent need of a flow chart for a light sensor that will work with > the i_Cube by Infusion Systems, like the one they sell themselves > (http://infusionsystems.com/catalog/product_info.php/cPath/24/products_id/51). > It just consists of a photo cell an a resistor on a small board, but I don't > know whether they're parallel or serially connected. the three cables are > the power, signal an ground connections. > > Any ideas how that could look when drawn schematically? I need to build a > lot of those, in the next few days... > I'm not that good at analogue electronics, so I'd appreciate any help, hints > or links to information (in english, german or french). Is there some sort > of archive for such things, or abeginners guide to some basic circuits?

Hi Tobias,

In the pdf there are 3 schematics. The first two are with foto resistors. In the left one, where the foto R is next to U+, the signal voltage gets higher (towards U+) when there is more light. In the right one, the signal voltage gets lower when there is more light. In general foto resistors are really slow so I'd recommend you to use foto transistors as shown in the third schematic (you can change R and FT in order to he inverse behavior). The value R depends on the Rf or FT, on U+ and the amount of light, I'd start with 1kOhm.

Andre

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On 29-dec-2006, at 14:00, Andre Bartetzki wrote:

> Es war der 29.12.2006 12:57 Uhr, als tobiasreber@freesurf.ch nicht > widerstehen konnte, folgende Gedanken dem Netz anzuvertrauen: > >> Hi everyone, >> >> I am in urgent need of a flow chart for a light sensor that will >> work with >> the i_Cube by Infusion Systems, like the one they sell themselves >> (http://infusionsystems.com/catalog/product_info.php/cPath/24/ >> products_id/51). >> It just consists of a photo cell an a resistor on a small board, >> but I don't >> know whether they're parallel or serially connected. the three >> cables are >> the power, signal an ground connections. >> >> Any ideas how that could look when drawn schematically? I need to >> build a >> lot of those, in the next few days... >> I'm not that good at analogue electronics, so I'd appreciate any >> help, hints >> or links to information (in english, german or french). Is there >> some sort >> of archive for such things, or abeginners guide to some basic >> circuits? > > Hi Tobias, > > In the pdf there are 3 schematics. The first two are with foto > resistors. > In the left one, where the foto R is next to U+, the signal voltage > gets > higher (towards U+) when there is more light. > In the right one, the signal voltage gets lower when there is more > light. > In general foto resistors are really slow so I'd recommend you to > use foto > transistors as shown in the third schematic (you can change R and > FT in > order to he inverse behavior). > The value R depends on the Rf or FT, on U+ and the amount of light, > I'd > start with 1kOhm. > > > Andre

one more thing: make sure that the circuit does not draw more current that the +5V lead can source. I would not go over 5 mA per lead, meaning that the resistor must be 1k or higher. for one LDR there is little risk of drawing too much current, but you mention that you are going to build a lot of them. how will you connect these? will each LDR circuit go to a separate iCube input? or do you want to send the combined effect of all photocells to a single input?

I am not sure if the iCube inputs are protected against overvoltage. If not: if you are going to use a second power supply for the photocell networks, (for example if you need more current) be sure that its output voltage does not got over +5V. It may help to clamp the iCube input to its own +5V with a diode.

-jennek

Es war der 29.12.2006 22:50 Uhr, als tobiasreber@freesurf.ch nicht widerstehen konnte, folgende Gedanken dem Netz anzuvertrauen:

> >> how will you connect these? >> will each LDR circuit go to a separate iCube input? >> or do you want to send the combined effect of all photocells to a >> single input? > > Olaf and Andre: thannks for the suggestions and pdf, I'll give it a try.. > > Jennek, I'll use separate iCube inputs for each sensor, so overvoltage > shouldn't > be a problem I hope. But thanks anyway for the hint.

If you use only the voltage provided by the iCube (probably 5V ?) there is no risk of overvoltage at all. But maybe too much current will be drawn if you connect many resistors with low values to the AD inputs of the iCube. The maximum current must be mentioned somethere in the manual. The current drawn with one voltage divider is the provided voltage (5V ?) divided by the sum of the two resistors (R and LDR). If there is much light the value of the LDR is very low so that the effective resistance is that of R. If that R is 1k the maximum current drawn by this one voltage divider is 5 mA (current = voltage / resistance) If the iCube has a maximum current of, lets say, 30 mA you can have 30mA/5mA = 6 voltage dividers of 1k. If you need more sensors you have to use 2k or higher resistors. But the higher the value of R the more you shrink the measuring range, so it's a trade-off between sensitivity and safety.

Andre

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