Hi, The circuit should look like something like this :
You also mentioned that I need to monitor voltages : *"An analog multiplexer driving an op amp running from 1.8 volts" * You mean that I need to use the onboard ADC ? But I have a problem, I don't know how to use such a system (mux + opamp). Could you explain me a little bit more please ? Thanks 2015-03-11 14:24 GMT+01:00 Harvey White <[email protected]>: > On Wed, 11 Mar 2015 12:41:40 +0100, you wrote: > > >Hi, > > > >Thank you for you response. > > > >I have a lot of 74xx components which may be dead. As my first project > with > >the Beagle, I would like to simply test the logic behind these chips > >(monitor the logic to detect wrong values). > > > >I first planed to wire the 74LS02 like this : > > > > > >But you mentioned that an output high ranges from 0 to 5v which could > >damage Beagle GPIOs (not 5v tolerant). > > > >If someone could give me more advises please ... > > If you're going to build an IC checker, then you need to think of > several things. > > 1) power and ground are in different places on several chip types > (7490 vs 7476). There are typically 14, 16, 18, 20, and so on logic > chips, look into ZIF sockets. > > 2) if you don't know the chip type, you can connect an output to a > chip's output. In that case, you'd like to have a passive (resistor) > pullup to the supply voltage, and an open collector output driving > that, and perhaps with a series resistor to limit current, since you > may be trying to pull an active output (that is high) low. Inputs > won't matter. > > 3) your pin driver also wants to be able to read the pin as well, so > the BBB needs the level translation back to the chip, the 8T245 would > work well there. > > 4) each driver needs to be individually controllable for both level > and direction. You need to be able to turn it off, set it high (10 k > pullup is ok, or set it low. In any of the above cases, you need to > be able to read the voltage at the pin. An analog multiplexer driving > an op amp running from 1.8 volts (or resistive divider in this case to > limit the a/d inputs to 1.8 volts max) would do well. That way you > can also identify a good or bad output, or just plain read the > voltages at the pins. > > more than you asked for, and more complicated, but the level shifting > is something to think about. > > it would be a nice project. > > Harvey > > > > > >Thanks > > > >2015-03-11 11:01 GMT+01:00 Eric Fort <[email protected]>: > > > >> first off, to properly answer your question we need to start by > >> referencing the datasheet for the part you wish to use found here: > >> http://www.ti.com/lit/ds/symlink/sn74s02.pdf > >> > >> something missed by many is that 3.3v OUTPUTS on a device such as the > >> beagle will drive standard 5v TTL logic just fine! just make sure to > limit > >> your fan out (number of logic loads) appropriately. The reason for this > >> becomes clear if one actually reads the datasheet referenced above for > the > >> part you wish to use. If you look at the 74LS02 VIHmin (the minimum > >> voltage which the input sees as high) it's listed as 2v. since 3v3 > > 2v0 > >> it works fine. the problem you have is that the output of the 74LS02 > >> swings from 0-5v so when the output of the 74LS02 goes high it will > measure > >> 5v. since 5v > 3v3 it will cook a 3v3 INPUT. So depending what you > want > >> to do you may or may not need voltage translation andin most cases (i2c > >> buses being the major place where you find an exception and do need > >> bidirectional) they need only be unidirectional and one may use simpler > >> circuitry such as a transistor or resistance ladder/voltage divider. So > >> I'll end by posing a question. What doyou want to accomplish with this > and > >> can you post a basic schematic for review for us tolookat and > >> constructively comment on? > >> > >> Eric > >> > >> On Tue, Mar 10, 2015 at 10:50 AM, <[email protected]> wrote: > >> > >>> Hi, > >>> > >>> I come from the world of sotware engineering and I am a newcomer > (nearly) > >>> to the world of electronic. I would like to know if it was possible to > >>> interface a 74LS02 to the BeagleBone Black. > >>> > >>> I plan to connect Vcc and Vss of the 74LS02 to the 5V Vdd output and > Gnd > >>> of the Beagle and use the GPIO pins to command the logic inputs. My > problem > >>> is that I don't know if I can plug the 74LS02 without components such > as > >>> resistors, in order to limit the current flowing through components. I > >>> don't want to damage the board. > >>> > >>> The result of all the logic operations should be gathered by some GPIO > >>> pins configured as inputs. > >>> > >>> Is it possible to proceed that way ? > >>> > >>> Thanks in advance for your answers > >>> > >>> -- > >>> For more options, visit http://beagleboard.org/discuss > >>> --- > >>> You received this message because you are subscribed to the Google > Groups > >>> "BeagleBoard" group. > >>> To unsubscribe from this group and stop receiving emails from it, send > an > >>> email to [email protected]. > >>> For more options, visit https://groups.google.com/d/optout. > >>> > >> > >> -- > >> For more options, visit http://beagleboard.org/discuss > >> --- > >> You received this message because you are subscribed to a topic in the > >> Google Groups "BeagleBoard" group. > >> To unsubscribe from this topic, visit > >> https://groups.google.com/d/topic/beagleboard/hTzOjUNwFZE/unsubscribe. > >> To unsubscribe from this group and all its topics, send an email to > >> [email protected]. > >> For more options, visit https://groups.google.com/d/optout. > >> > > -- > For more options, visit http://beagleboard.org/discuss > --- > You received this message because you are subscribed to a topic in the > Google Groups "BeagleBoard" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/beagleboard/hTzOjUNwFZE/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > [email protected]. > For more options, visit https://groups.google.com/d/optout. > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. 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