Hooking up a seven segment LED display
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- Опубліковано 14 лип 2024
- I thought it'd be fun to hook up an old fashioned 7 segment LED display using the driver IC that came in the TTL chip kit!
[This is my first attempt at a 4K video (still using an iPhone and a Yeti, but this time I captured with reincubate.com/camo/ instead of OBS). I also tried to improve(?) the audio levels in this one, but i find that whole a process a bit of a dark art so I don't know if it worked out or not.]
-- Links
7 Segment Display Data Sheet: www.xlitx.com/datasheet/5161AS...
SN74LS48N Data Sheet: hlf-ic.cn/upload/202108/SN74LS...
7 Segment Display: amzn.to/3viAu1l
TTL ICs: amzn.to/40WH75c
Breadboard kit: amzn.to/3MYwfho
Power supply: amzn.to/3uAYxIE
Antistatic mat: amzn.to/49RhcQi
My Wife's Books: amzn.to/47yt9Ji
(Maybe you and/or someone you know will like them!) - Наука та технологія
I think of LT as "Light Test", as it turns on all LEDs and is useful to ensure an LED didn't burn out. A typical use-case is that this pin goes low on device power-up to let the user see if all LEDs go on or not.
Something I recommend for the future if people are trying to learn from your videos it might help them if you linked the documentation you used in your video. Love this channel
Ah yeah, thanks! I updated the description with some more links.
@@bigzaphod ofc!
3:01 The pinout on this 7 segment display actually makes sense.
a 7 segment display always has the segments labelled as A to G, where A is the top part, then the letters ascent as you follow the segments around clockwise, with G being the middle one.
The pin numbers start at the bottom left pin, and are numbered ascending anti-clockwise.
So if you ignore the pin numbers, and accept that the top and bottom middle pins are common, then pin A would be the one to the right, of the top middle pin, which is 7, and it is!, follow this around, and with the gap at pin 5 being the DP, as that is placed to the right of segment D, the segments do align with the pins you'd expect... near enough.
6:15 again, look at the pinout of the chip, and compare it to the pinout of the display. F and G on the display roll around back to the other side of the pins, so if you were reading the pins clockwise from the top left, it goes F, G, (common), A, B, DP, C, D, (common), E, F. Ignore the common and DP, and you get the same F, G, A, B, C, D, E as on that side of the chip. This makes routing the output of the chip to the display on a PCB easier.
8:10 My programming lecturer used to call this "Klingon". If you actually draw up a karnaugh map of 4 inputs to 7 outputs for 0 to 9, and ignore the possible inputs for 10 to 15, making the circuit as simple as possible to achieve this task, you do end up with mostly nonsense for those last 6 positions. I think 15 is blank on the 74LS47 (which I used in some of my projects) so I'd often use this as "Off". Looks like when you set your 74LS48N to the same, it also went off, so it's probably just the same circuit with inverted outputs.
8:43 I have no idea what those pins do by those descriptions! From using the chip previously though, One pin should be output enable (so it turns the display off), and another is a latch control (so it holds the same number even when you change the input), I'd see if there's a logic table somewhere on the sheet, it probably tells you what the outputs do when you change each of these. From your playing around, the other of those 3 pins looks like it turns all the lights on.
very nice to see how enginering tasks are dealed with in realtime. And semi-high video quality, no wonder why youtube showed it to me. Wish you high stats
RBI/RBO are used to eliminate leading zeros, e.g., suppose you have 3 digits. It is preferable to see 0 rather than 000 or 7 rather than 007.
Ooooh! Well that suddenly makes a lot of sense!
@@bigzaphod in datasheet shows a diagram - it clearly and graphically shows what these inputs/outputs do. 🙂
Idea for counter: a small 555 chip circuit could provide slow pulse which somehow advances the number on the display 0-9 in a loop. I think a "CD..." counter chip would be more suitable for this purpose. 😉
Do yourself a favour and download the Texas Instruments version of the datasheet. It's much easier to understand than the Chinglish HLF one because it was written by a native English speaker. LT means lamp test and it does as you saw - it lights up all the segments. RBI and RBO are ripple blanking in and out. The purpose is to suppress leading zeroes in multiple digit displays. For example, on a four digit display 42 looks better than 0042.
That chip you have is called a bcd to seven segment converter. For bigger values you need to attach a binary to bcd converter to several bcd to seven segment converters.
Bread boards are for slicing fresh bread. Love the exploration. Cheers.
this video is a bait and switch.
there is no 7 segment display made of 7 of 7 segments displays, like in the thumbnail
My entire life is a lie
It shouldn't be too hard to make one. The real question is, if you display a number, should each one show that number as well (how?), or should each one that is on show 8 or something instead?
Google for "Clock Is Made Out of 144 Seven-Segment Displays "
3:01 you can see the PIN numbers in the LED diagram.
your video is really good but i have a little suggestion can you make a little bit faster topic by topic
You can use a 74LS93 with a clock input to count 0-F in 4 bits and cycle automatically. I'd link to a vid but YT will just kill my comment (again). All I can say is Haseeb Electronics.
first time seeing the bcd to 7 seg working.
The BCD simply displays one digit and connects to a decimal counter that counts from 0 to 9, but not to 15, as 4 bits allow.
10:55 you can hook up several of those chips to get multiple digit displays.
Can't claim any electronic expertise, but I can claim to have a preference for how '6' should be displayed on a 7-segment display and this display chooses the "wrong" one for my taste! That is, it looks more like a lowercase b.
More advanced seven segment displays (or rather, I assume, the underlying drivers) tend to display the digits greater than 9 as A, b, C, d, E and F, (note the case on b, d and possibly f), so this driver chip is clearly only for 0-9, because the appearance of 6 collides with what would be b.
As another commenter points out, the outputs it gives for the values greater than 9 are probably just whatever garbage is caused by the logic for the valid values. I wouldn't be surprised if there's a version of the driver chip with the aforementioned extra states baked in, as well as a "fixed" (in my opinion) 6, but that won't be as, uh, cost-effective as this one.
Do you ever plan to get into arruino or do you expect to continue down just moving electrons without coding?
Another thing is as long as your resistors have a high enough wattage you can save space by only hooking up the resistor to the negative side (I have seen no bad effects from doing so)
Not sure, tbh! I started this series with the idea of eventually hooking up an old 8-bit processor chip I found, but also to kind of get a more intuitive feel for how stuff actually works underneath the code.
@@bigzaphod I totally get that!
8:19 that is just random values because of how the logic works.
LT = Lamp Test
The blanking feature didn't work because you forced it to not work by tying the blanking output high. It's a terrible idea to connect anything labeled as an output to high or low. Best case, you get bad behavior (which you saw). Worst case, you fry something in the chip (and you get bad behavior)
Oh wow.. I didn't realize that one pin was even an output. Looking at it closer, it seems like it is perhaps either an input *or* an output depending on the state of some other pins? No wonder it didn't make sense!
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