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Topic: Combining analog input (Read 2 times) previous topic - next topic


That makes sense. I wish somebody told me that here. But I'm glad I you told me this while its still on my breadboard :) I just dont get it why they didnt mention to put transistors between it in the playground example.  :smiley-sweat:

So todo for now:
* Add transistor to the rows.
* Add a Multiplex. (4051)


I just dont get it why they didnt mention to put transistors between it in the playground

Sadly it is not a very good example, you will note there is no resistors in although the text now tells you to do this after some badgering from a few members. The lack of resistors and overwriting of the outputs probably meant the display looked ok. There is a train of thought that goes, it is only a demonstration and people will not run it for long so overload dosn't matter.
However I think that it is important to get it right as people, like you, go on and use the circuit as a basis to expand into their own design. If you start off with the right idea you don't have to relearn old stuff.


Mar 05, 2011, 03:00 am Last Edit: Mar 05, 2011, 03:02 am by DragoslaV Reason: 1
Thanks everybody and thank you Mike for clarifying that out!

Based on your input and based on this schematic, I have created a new schematic for myself including the multiplex and transistors. The transistors used in this schematic is a '2N3904'. Could I also use this for my setup??

Also I would love to hear if I made a(nohter) mistake in my schematics!  :D


The big block labaled transistors represents 6 more of the NPNs above?
You are missing the resistors between the arduino and the base pins as shown in the example you cite.
Need them to limit current out of arduino pin.

You might also look at ULN2803, 8 transistors all packaged up with needed resistors.
High input pin, output pulls LED cathode low.
ULN2803 is 46 cents at dipmicro.com
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.


Mar 05, 2011, 02:19 pm Last Edit: Mar 05, 2011, 02:30 pm by DragoslaV Reason: 1
Yeah, that block should have represented 6 more of the NPNs like above. To be honest the new program I was using is frustrating as hell to work with so I just made it one block  :smiley-roll:

Also thank you a thousand times for the ULN2803A tip! This will definitely save me time and wires! I'm now off to the store to buy the 4051 and the ULN

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