On Tue, 13 Feb 2007 05:31:57 +0000, Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:> > >panfilero wrote: > >> Hello, I have a question about driving an LED with a 7406. > >What on earth are you using a 7406 for ?--- Read the fucking thread, why don'tcha? -- JF
driving an LED with a 7406 question
Started by ●February 13, 2007
Reply by ●February 13, 20072007-02-13
Reply by ●February 13, 20072007-02-13
John Fields wrote:> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote: > >panfilero wrote: > > > >> Hello, I have a question about driving an LED with a 7406. > > > >What on earth are you using a 7406 for ? > > --- > Read the fucking thread, why don'tcha?There is nothing in the original post to indicate a reason for its use thank you very much Mr Allegedly Polite ! Does anyone even still make a standard TTL 7406 ? It seems unlikely to me. Graham
Reply by ●February 13, 20072007-02-13
On Tue, 13 Feb 2007 11:44:44 +0000, Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote:> > >John Fields wrote: > >> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote: >> >panfilero wrote: >> > >> >> Hello, I have a question about driving an LED with a 7406. >> > >> >What on earth are you using a 7406 for ? >> >> --- >> Read the fucking thread, why don'tcha? > >There is nothing in the original post to indicate a reason for its use thank you >very much Mr Allegedly Polite !--- Geez, I thought from his post (which included a diagram, BTW) that he was using it as a low side LED driver and wanted some help in figuring out the value of the current limiting resistor. --->Does anyone even still make a standard TTL 7406 ? It seems unlikely to me.--- Who cares? It's what _he's_ using. -- JF
Reply by ●February 13, 20072007-02-13
> Who cares? It's what _he's_ using.Thank you JF. I appreciates everyones concern over the components I'm using, but I'm not looking for a more efficient design to this simple problem, I was looking for some understanding to these kind of simple circuits. This problem is just for helping myself understand things not for efficiency or pratical use in any specific application. Thank you
Reply by ●February 13, 20072007-02-13
John Fields wrote:> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote: > >John Fields wrote: > >> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote: > >> >panfilero wrote: > >> > > >> >> Hello, I have a question about driving an LED with a 7406. > >> > > >> >What on earth are you using a 7406 for ? > >> > >> --- > >> Read the fucking thread, why don'tcha? > > > >There is nothing in the original post to indicate a reason for its use thank you > >very much Mr Allegedly Polite ! > > --- > Geez, I thought from his post (which included a diagram, BTW) that > he was using it as a low side LED driver and wanted some help in > figuring out the value of the current limiting resistor.Well ? So ?> --- > > >Does anyone even still make a standard TTL 7406 ? It seems unlikely to me. > > --- > Who cares? It's what _he's_ using.Do you never think to offer advice about component selection ? Graham
Reply by ●February 13, 20072007-02-13
Reply by ●February 13, 20072007-02-13
On Tue, 13 Feb 2007 11:44:44 +0000, Eeyore wrote:> > > John Fields wrote: > >> Eeyore <rabbitsfriendsandrelations@hotmail.com> wrote: >> >panfilero wrote: >> > >> >> Hello, I have a question about driving an LED with a 7406. >> > >> >What on earth are you using a 7406 for ? >> >> --- >> Read the fucking thread, why don'tcha? > > There is nothing in the original post to indicate a reason for its use thank you > very much Mr Allegedly Polite ! > > Does anyone even still make a standard TTL 7406 ? It seems unlikely to me. > > GrahamYes http://focus.ti.com/docs/prod/folders/print/sn7406.html
Reply by ●February 13, 20072007-02-13
On Feb 12, 11:00 pm, "panfilero" <panfil...@gmail.com> wrote:> Hello, I have aquestionaboutdrivinganLEDwith a 7406. Basically > I have an MCU going into a 7406 inverter going into anLEDgoing to a > resistor R and that going to a 5 V power supply. All in series, and > I'm trying to find the value for R that would make this thing work.... > here's a sketch of what I'm talking about (this is my first time > skecthing on notepad) > > o 5 Volts > | > | > | > / > \ R > / > \ > | > | > __ > \/ LEDMV5353 > --- > ------- | > | | | > | | |\ | > | | | \ | > | MCU |-----------| \-----------------| > | | | / > | | | / > | | |/ > | | > ------- 7406 > > This is how I began to tackle this problem: for MCU output = high I > looked on the spec sheet for theLEDit said that theLEDuses a > continuous forward current of 20 mA at a voltage drop of 3 Volts. > Then I went to the 7406 specs sheetand looked up IOL = 40 mA. So I > think to myself.... great, it can sink 40mA and I only need 20mA. so R > = (5-3)/20mA = 100 Ohms.... now I just have to check R with MCU out = > low.... > > I start to get stuck here, cause I begin to think.... should I include > VOL as a voltage drop when finding R? shold R = (5-3-VOL)/20mA ? Cause > I'm thinking VOL is the voltage drop for the 7406.... but I look on > the spec sheet and there's 2 values for VOL = 0.7.... > > so R = (5-3-0.7)/20mA = 65 Ohms > > so.... when MCU output = low.... I'm not sure what to do here.... I > look up VOH.... VOH = 30 Volts.... whoa! hmmm..... I look up IOH, IOH > = 0.25 mA....... and then i think, i've got 25mA going towards thatLED, but wait.... it's going the wrong way, theLEDwill stop it... > but I wonder how much current theLEDcan stop? > > at this point I'm totally confused and am not sure if I'm looking at > things the right way anymore, the VOH,IOH,IOL,IOH stuff is confusing > to me..... can anyone tell me if I'm on the right track? > > thank you > Joshua > > so for MCU = low: I guess I need to find IOH? That's IOH = 0.25 > mA.... I'm not sure what to do next, should I look up VOHThe first thing I sometimes do, is take the LED and see how much current it needs to be bright. I'm not talking about lighting up the room either. I usually use between 5 an 10 ma. max for indicators. Back in the old days you needed the current for a little brightness. greg
Reply by ●February 13, 20072007-02-13
On Feb 13, 9:14 am, "panfilero" <panfil...@gmail.com> wrote:> When the 7406 is off, can I treat it as a 0.7 Voltage load with 40 mA > running through it to ground?It can be hard enough to explain this sort of design in person, much less by group postings, but I'll give it a try. The 7406 or any other switching device has two sets of ratings; one for input and one for output. The input specs tell you what is required to drive the inputs to a valid state. The output specs tell you what sort of load and voltage can be driven by the output. The LED requires about 20 mA at about 2.2 volts to drive it. If you use a 5 volt supply and use a 74LS06 as the control (I can't find a data sheet on the 7406) you need to subtract the LED voltage and the 74LS06 output voltage (VOL@24 mA = 0.4V) from the power supply to find the voltage on the current limiting resistor. 5 - 2.2 -0.4 = 2.1V. At 20 mA this will give you 2.4V / 20 mA = 120 ohms. Since this is an open collector device, it will not source any current to the LED, so you don't need to worry about that. The IOH of this device is not given because it does not drive current when the output is high. Regardless, IOH and IOL are maximum values or conditions for measuring VOL and VOH. The outputs of digital devices are just transistors connected to ground and power; they are not current sources. They provide a voltage and the current drawn from the output is determined by the load. In the above example I only needed to know the current into the 74LS06 output because there is some resistance in the transistor connection to ground so that the output voltage of the 74LS06 depends somewhat on the current flowing. At 24 mA the output voltage is 0.4 V, at 48 mA the output voltage is 0.5 V. You can see this is not a large difference. Even a microAmps of current, the output voltage will likely be around 0.2 volts. For most circuits you can estimate the output low voltage to be about 0.4 volts for TTL type devices. CMOS devices are much more like resistors on the output so the resulting voltage varies directly with the current. Does that help?
Reply by ●February 13, 20072007-02-13
On Feb 12, 11:00 pm, "panfilero" <panfil...@gmail.com> wrote:> . . . so R > = (5-3)/20mA = 100 Ohms.... now I just have to check R with MCU out = > low.... > > I start to get stuck here, cause I begin to think.... should I include > VOL as a voltage drop when finding R? shold R = (5-3-VOL)/20mA ? Cause > I'm thinking VOL is the voltage drop for the 7406.... but I look on > the spec sheet and there's 2 values for VOL = 0.7.... > > so R = (5-3-0.7)/20mA = 65 OhmsOne approach is to try the larger resistor value (100 ohms) and measure the current. If you're wrong, then you'll get too little current. But it WON'T fry any of the components, and you can then get a better idea what the correct resistor should be. Sometimes a little experimenting helps more with learning electronics than spending a lot of time getting the calculation correct. Mark p.s. to measure the current, I'd measure the resistance before putting the resistor into the circuit, and then measure the voltage drop across the resistor while running the LED. But that's just my preference, I tend to avoid using ammeters directly.
