Another question on parts...

Hi,

The ULN2003 and its later derivatives, can be examined/downloaded here for example:- (but there are many places to find similar info’s)

http://www.datasheetcatalog.org/datasheets/1150/489336_DS.pdf

They are most useful in driving smaller loads. Do remember that on some versions, although you have theoretically 7 x 0.5 amps (3.5 amps total), you must actually use far less as the total heat dissipation does not allow 3.5 amps, often only 2 amps…….this catches a lot of people out. Do heat-sink the chip or use a tiny fan to cool it (or both!!) if you are running near its thermal limit. Different versions can supply more current, so shop around.

It’s probably best to have a 12 volt supply and use a separate regulator to make from this 12 volts  supply, the 5 volts for the Arduino.

Depending upon the total amounts of current required, sometimes even a “Wall-Wart” like the one you mentioned will supply may be strong enough!!! Though I do recommend a quality one using a switched mode as they are exacter and run cooler…..they are also more energy efficient, which can become quite important if this will run 24 x 7 for example. I never use anything else….

The one you depicted does not appear to be switched mode and may run hot and be far less efficient. Also some of these supplies are of very poor quality and supply voltages far, far away from the marking, usually very high especially when lightly loaded…..do always check the unloaded voltages with a good meter, you may be in for a shock. Some SMPSs need a slight load to run correctly voltage wise too……

Do get one with switched mode…..they generally last longer too!!

I buy Laptop power supplies from ebay, sometimes for only €1 (Plus €4,50 postage!), which are always switched mode, small, very energy efficient and can supply between 4 and 5 amps generally.

Here is one delivering 12 volts at 3 amps for very little money!!:-

http://cgi.ebay.co.uk/12V-ASUS-EEE-LAPTOP-AC-ADAPTER-POWER-SUPPLY-CHARGER-/270698521966?pt=UK_Computing_LaptopAccessories_PowerSupplies <http://cgi.ebay.co.uk/12V-ASUS-EEE-LAPTOP-AC-ADAPTER-POWER-SUPPLY-CHARGER-/270698521966?pt=UK_Computing_LaptopAccessories_PowerSupplies&hash=item3f06e3a56e> &hash=item3f06e3a56e

Best wishes

Andy M.

They are most useful in driving smaller loads. Do remember that on some versions, although you have theoretically 7 x 0.5 amps (3.5 amps total), you must actually use far less as the total heat dissipation does not allow 3.5 amps, often only 2 amps…….this catches a lot of people out. Do heat-sink the chip or use a tiny fan to cool it (or both!!) if you are running near its thermal limit. Different versions can supply more current, so shop around.

It’s probably best to have a 12 volt supply and use a separate regulator to make from this 12 volts  supply, the 5 volts for the Arduino.

OK, im very confused now :-)

In the above linked blog posts ect, they are using ULN2003, are you saying that if I do use one, I need to cool it?

And its probably just me being thick, but I am still no clearer on which model I should use and what the differences are, I read the PDF but if I am honest, am still no clearer.

A link to the correct one would be great (and explanation why would also be helpful.)

PS, thanks for the advice on the power source.

They are most useful in driving smaller loads. Do remember that on some versions, although you have theoretically 7 x 0.5 amps (3.5 amps total), you must actually use far less as the total heat dissipation does not allow 3.5 amps, often only 2 amps…….this catches a lot of people out. Do heat-sink the chip or use a tiny fan to cool it (or both!!) if you are running near its thermal limit. Different versions can supply more current, so shop around.

It’s probably best to have a 12 volt supply and use a separate regulator to make from this 12 volts  supply, the 5 volts for the Arduino.

OK, im very confused now :-)

In the above linked blog posts ect, they are using ULN2003, are you saying that if I do use one, I need to cool it?

And its probably just me being thick, but I am still no clearer on which model I should use and what the differences are, I read the PDF but if I am honest, am still no clearer.

A link to the correct one would be great (and explanation why would also be helpful.)

PS, thanks for the advice on the power source.