Basic Stamp2 question
lobo
Posts: 100
How much current can one pin on the basic stamp2 handle?
The reason i ask is because I am going to build or want to build an irledemmiter/detector circuit that will will have 6 irleds (each on one side forming a circle)and one detector in the middle.
First, I want to connect the irled in this manner: - to - and + to +. Is this correct?
Second, I want to connect only one resistor for all of them and connect the other end to a pin on the Basic Stamp. Is this correct. Can·I do·this?
Third,·I·know that connectingd irled·in series will add current but i figured that by using·the right resistor·I could bring the current down to an acceptable current·for the Basic Stamp 2. I this train of thought correct?
Now, you might ask why are you doing this? Well I will tell you why, because·I just want to. O and the experience of working on circuits wether done right or wrong doesn't hurt. Really, that's the reason why·I'am doing this. You know what·they say, "·practice, practice, practice."
Plus, i will inform ya if it worked (if·it can be done with the basic stamp-pending on yas·info)·if it makes any difference at all having 6 irleds/one detector versus 1 irled & 1 detector or not.
If you give me the green light and tell me it can be done· without harming the basic stamp2, i will inform as to in what way it made a difference.
thanks for yas responses.
·
The reason i ask is because I am going to build or want to build an irledemmiter/detector circuit that will will have 6 irleds (each on one side forming a circle)and one detector in the middle.
First, I want to connect the irled in this manner: - to - and + to +. Is this correct?
Second, I want to connect only one resistor for all of them and connect the other end to a pin on the Basic Stamp. Is this correct. Can·I do·this?
Third,·I·know that connectingd irled·in series will add current but i figured that by using·the right resistor·I could bring the current down to an acceptable current·for the Basic Stamp 2. I this train of thought correct?
Now, you might ask why are you doing this? Well I will tell you why, because·I just want to. O and the experience of working on circuits wether done right or wrong doesn't hurt. Really, that's the reason why·I'am doing this. You know what·they say, "·practice, practice, practice."
Plus, i will inform ya if it worked (if·it can be done with the basic stamp-pending on yas·info)·if it makes any difference at all having 6 irleds/one detector versus 1 irled & 1 detector or not.
If you give me the green light and tell me it can be done· without harming the basic stamp2, i will inform as to in what way it made a difference.
thanks for yas responses.
·
Comments
Since most IRLEDs have a forward voltage of 1.7V, you could connect two in series for a total drop of 3.4V which you could drive from an I/O pin. You would need I believe a 68 ohm series resistor for the two series LEDs for a current of 20ma (with a HIGH voltage of about Vdd-0.3V = 4.7V). If you want to put two of these strings of two LEDs in parallel, you would have to reduce the current to about 10ma each with a 130 ohm resistor. You must have a resistor for each string of two LEDs. Otherwise it's possible for one string to have a slightly lower forward voltage and that string will hog the current and possibly overload the LEDs or at least have markedly different brightness.
The stamp pins (and I don't know this for sure if there is a schematic for the stamp) but I think only portC and portD make up the 16 pins so looking at the maximum one pin can sink (25ma) only two pins on that port can be used to sink 50mA using pin 0 and pin 1 (I think are on port A) you can run 2 strings at 20ma each and then use one of the pins 8 thru 15 for the last string of 2. The maximum current out the VSS pin (going in a pin it goes out the VSS pin) is 150mA so three strings would be 60mA going out, remember if you have other stuff to run you will have to add that and not exceed 150mA. I don't think you should exceed 70% of the absolute maximums and this much current though still small should be done through transistors or fets.
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