MitchElectronics - Logic Probe Kit

hello my name is Rob Mitchell and welcome to EFM electronics for makers in this episode we're going to be looking at another Mitch electronics kit the logic probe we're going to see how it works why it works and what you can do with it [Music] [Music] [Music] now when it comes to debugging circuits it can be a tad tricky trying to figure out what logic signals are doing you could use an oscilloscope in actual fact that would be one of the ideal tools that and a logic analyzer which allows you to analyze logic signals over a very small period of time but these can be very expensive for example an oscilloscope can cost you five six hundred pounds of ones it gives you dot anywhere between two and four channels but sometimes what you read is just a simple quick tool to know if something's on-off oscillating or floating and this is exactly what the logic program expect Ronix does so the logic probe consists of two main sub circuits the first one being a simple inverter configuration here and then two other inverters here what they'll say the inverters they are actually nor gates but most of them have been configured to be an inverter with the exception of you won't be now the input comes into this nor gate here which has been configured as a not gate so we're going to go and draw it like so and you'll see there is a 2.2 mega ohm resistor going across like so input and nature outlet now what this is doing is quite interesting if the input is connected to absolutely nothing this 2.2 mega ohm resistor acts as a feedback resistor and cause the output to oscillate only a very small solution and would be very hard to actually record it on an oscilloscope if you had like the old-fashioned ones on in digital one or a more precision one you would be able to see this but on a typical one you would you know you would what unit it's hard to measure because of the magical stuff anyway now so if the input is floating the output has a tiny oscillation if the input is connected to zero volts which would be a zero a logical zero the output would be high that's good to zero that ship let's just try this is a natural graph via zero volts there I get five volts and if the inputs was five volts or logical high doesn't really matter it could be 5 volts 3 volts then you get 0 and if the input was oscillating which means it's doing this between 0 and 1 then the output pause has a big oscillation now it's important to realize that this is a big oscillation between the maximum voltage of this of the circuit and the minimum voltage being zero but the tiny oscillation isn't it oscillate around the midpoint of the voltage like that so if this is zero volts down here that was be down there this peep out VC if you've out V divided by 2 so it's going to be like let's say if we power the logic pro with a 9-volt battery it's going to oscillate about 4.5 volts it's very very tiny tiny oscillation now depending on the output these two LEDs here the d2 and d3 will do whatever it is that they need to do now depending on the output of this little inverter configuration will either turn on or off these LEDs if the input to this system is high then the output becomes low or essentially zero volts which means that d2 turned on because current can go through VDD through d2 and into the inverter configuration if the output of this is high that means that D - turns off because you know current can't flow back into it but current can flow out of that inverter go through d3 into ground so d2 turns on when the input is on and d3 turns on when the input is off if the input is oscillating then both of these diodes are going to turn on because for half the time that one we turned on and for the other half of the time the other won't be turned on but you must also understand that the brightness of d2 and d3 which represent on and off respectively also relate to the duty cycle such that the higher the duty cycle where your incoming wave looks more like this then d2 is going to be more bright than d3 because it spends more as time being on than the 3 and due to perspective or what's it called is the thing with image of the eye is persistence of image or something so this configuration allows us to see on off and oscillating but what about floating this tiny little oscillation when this thing is floating the output of the first inverter is going to be around the 4 point 5 volt range if it's powered by 9 volts so half the supply that means neither of these two LEDs can turn on however this time the oscillation is enough to trigger this monostable circuit configuration here which causes the output of this to also change now the purpose of the monostable circuit here is twofold the first one is to slow down oscillations and this slows down fast oscillations to slower oscillations so that you can power an external led and the second purpose of this little Manas table is to be able to detect the floating now if a digital signal is oscillating this configuration here can slow down that signal for displaying on the last LED and the second purpose for this Manas table is to detect the little floating oscillations here such that when the input is floating and you get the tiny oscillation it's not enough to turn on D 2 and D 3 but the monostable is sensitive enough to pick that up and so when the input to the monastery was a tiny little signal like that coming from the floating stage that gets turned into a nice big changing slow signal which causes D 1 to turn on so if we look at our LEDs we have the red yellow and the green and depending on their configuration will mean different things so if they're all off well you haven't powered you if your logic probe if the red one is on and everything else is off then what you've got is you've got a logical zero it's going to be signal if red is off yellow is on and green is off then you've got a floating signal high impedance if only the green is on then what you've got is a logical one and if all three are on then you've got an oscillating signal and that is the logic probe so now that we know how this works let's build it so as with any other electronics project the first thing you're going to do is check you've got all the parts and download the schematic and make sure they're all matches up so this is the kit you get from Mitch electronics it's in a foil bag everything is protected in static wise which is always good go ahead open up all the parts out left in the back that's fine and that can be reused for something else actually in terms of keeping and storing components so let's build it first thing I like to do always is the icy sockets the reason why I tend to do I see sock is first and not resistors is because I like I like used to be put on absolutely immaculate II nothing here it takes me more than having a ICS ocular slightly off so what I like to do is like to go ahead and solder the top right or top left pin and then the bottom pin and then underneath as you can see it's not actually on never at all my finger here and like that and we have the thing perfectly like perfectly flat I got this soaring line actually from D I call it diddly-dee little if you don't get the reference basically the diddly deee joke is something from Mitchell and Webb long story short it's quite funny to watch that you have to just just google diddly deee you'll see what I mean anyway so from the see I got the soldering iron from middle it's actually a really good i'm the tips are terrible so i'm gonna buy some new tips that don't have the screw top because he's actually use a screw to fix in and then what i'm gonna do is i'm going to thread that with an m4 thread so i can use a different type of tip i will essentially make your own tip your sorta line so just quickly go through all of these and get them sold it up you'll notice the lack of an extractor fan I'm not that picky i don't do enough soldiering to justify it to be honest so the next part I'm going to do now are the resistors so many the first the first I'm going to do the first three 1k resistors first and I believe those are our five r1 and r4 five justic bears are in now interestingly most people tend to pull pins outwards I find that if you pull the pins inwards like so you can actually fit quite a lot of resistors at the same time other way otherwise if you bend them outwards you've got a resistor next to it you can't do them both at the same time I'm gonna go ahead take that one as a humungous be in the workshop is huge I'm not gonna lose the cameras thing keep it there ask what happens when you live in the countryside you have flies B's and C's coming through the window all the time right so now that it's all done it's gonna go any soldier who's up the the fact that my tip is basically deteriorate it makes it quite different disorder but in all fairness when the soldering iron does work it does a really good job I mean I sets like 450 degrees and set the Celsius you know in it it does sold it really well if the solder sort of goes very very liquidy and flow is quite nice like that you see so it just really does the job well and it's not too harsh components but you may want to turn it down if you're gonna do something like a transistor it all fades I've never actually done it apart through heat I mean I've I think you'd be huh they always moan about putting heat sinks on drugs just when you solder them but I think I think you'd have to be very very silly to actually be able to damage am yeah you'd have to be very silly to damage a part by heat I believe right so now we're going to put on the 2.2 mega ohm resistor which is r3 this is the input resistor that formed our week is the week off space I think it's a week off idea you'll notice at this time I've just done the end I just did the resistor legs going out because there are no other neighboring resistors there was like the loads of resistors on this board all packed together I then push them instead of out and then the last one is the 4.70 mega ohm resistor in the camera now like that the 4.7 mega ohm resister is that we've got two capacitors both the same value soap doesn't matter which way you put them in because they are ceramic of equal value like so haha that one's in [Music] and that one too and I keep knocking the spunda that's one of the criticisms of this soldering station is at the sponge sits on a tiny metal place not even held in properly I have all of one of those brass sponges because I'm getting ready for it I've been using the ones I mean this thing does it Rex it's absolutely ready for Chisolm the second x-ray yes which is I can't even get pointed give that about 30 seconds to heat up because it's a new chisel bit it's not going to be exactly perfect it might make things a little difficult when trying to solder because it's so flat she's also gonna get in the way a little bit all right I think that's had enough time let's go ahead and tin this thing for the first time all wow it's changed cut of the disaster okay you can yeah that's really like phobic just try so oh wow that's done a really good job okay flip this round yeah really good I should use a holder for this but I can't be bothered to get one twice ever find a bit irritating and constant have to take it off the stand all the time i mean i don't i know this soldering jobs probably the worst wasn't may have done but i've never read this in front of a camera so so that's that part done i'm gonna go ahead and put the leds in so you've got the on which is our green it's just I'm an idiot that green is now in we've got the yellow which is the oscillating is actually technically floating yellow oscillating when they're all on and then weird like that looking pretty good go ahead and just sort of ease huh this is a classic example of why our very hot iron can be very beneficial even though very high temperatures can potentially damage components it the solders become so liquid in it it's very much a here's to anything so it's definitely worth the risk yeah my Stephanie set to put more than 450 actually Celsius here I know it's very hot but um oh definitely does the job yes done the job very well now the last part to add what we're gonna add is the Pogo pin and you might be wondering why this board has a Pogo pin instead of just am a solid piece of metal one of the nice things about Pogo pin is that it can basically take the mechanical stress of a connect of the connection here so this is gonna be soldered directly to this pad here now this was just a solid pin and you push into something it can basically it and you know cause fractures and the solder so using a Pogo pin means that when you push in it actually puts takes to stress and puts it into the spring so it takes the stress off the joints and essentially dramatically increases the length of life of this thing so the first we're going to do it's gonna be a little complicated and a holdest fan with this thing here I'm gonna tin this pad yeah we're gonna hold up yeah that's good that's good as you can see the pad day we don't want the pan gets the solder it goes onto a straightaway I'm going to go ahead and solder the end of the Pogo pin now these pogo pins are gold-plated so they should be moved very much wanted yet exactly wanting to have salt on them and we're going to hold the Pogo pin very quickly and I melt this pad first there we go make sure the pin is straight as well and that pins gonna get very hot very quickly inaudible well there's a new use for the chisel with keep it in person anyway yeah now might be angled this way but oh that's pretty good very great that's really good now the last stage is to put the wires on but I'm not gonna bother with that just for now I just wanted to sort of see how this would go together and we can go ahead and take the chip off and put it into our ship holder now the way I like to put chips in like to put them flat like this and bend them forward ever so slightly because chips when they're brand new it is this is actually one way you can tell a chip it is brand new I'm not ripped off or you know I'm not going to pull it out for some where the pins tend to be splayed outward slightly if it's been used they'll be directly straight down like this one so I've bend them down straight so they go into the end of the socket better like so we are all done with magic probe well that's all we have time for today for this episode of EFM thanks for watching and see you next time

Channel: EFM: Electronics For Makers

Views: 2,651

Keywords: Logic, Probe, Kit, Electronics, electronic kit, diy, mitchelectronics, how-to, build

Id: 6gYaYhbVMM0

Length: 18min 55sec (1135 seconds)

Published: Thu Aug 29 2019