49 votes
Accepted

Why did my LED resistor burn while lighting four LEDs in series?

6.8 volts seems awfully high for a single LED. Are you sure that 6.8 is not the number for all four LEDs? That would make it 1.7 volts per LED, which is more reasonable for a red LED. And that would ...
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  • 2,398
40 votes

Why did my LED resistor burn while lighting four LEDs in series?

I see your problem. Your circuit shows how you're driving a single LED segment. (I presume you then have 7 of these circuits, one for each segment.) The datasheet shows 4 LEDs in series, covering ...
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  • 5,719
28 votes

Why does the seven segment display have decimal point at the right?

Figure 1. Vertical display. Source. Figure 2. Slanted display. Source. Reasons for slant: '7' in particular, '4' to a lesser extent and perhaps '2', '3', '5', '6' and '9' all appear more natural ...
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  • 159k
26 votes
Accepted

Why does the seven segment display have decimal point at the right?

I think mike65535 is probably correct, more-or-less. Of course the argument that there's room on the right of the digit and not the left only makes sense if the digit is slanted to the right. There'...
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19 votes
Accepted

Seven-segment display seems to draw little current

First of all +1 for measuring your display. Too often we get questions here about "I saved money by buying cheap from Alibaba but it don't work. Now please spend you valuable time helping me out". ...
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  • 14.1k
15 votes

7 segment binary to hex

Find what museum is missing their 74xx logic ICs and return them. Then get a small microcontroller and do all this in a single chip. As a bonus, you'll be ready for other advanced projects from the ...
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11 votes

7 segment binary to hex

Maybe, if you feel particularly adventurous, you could even use a diode ROM, with perhaps two 74'138 3-to-8 line decoders to decode/drive the stuff. :) Here's a crude schematic of the whole ...
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9 votes
Accepted

Why does this 7-Segment Display not function properly?

The 74LS47 shows the following: $$ \begin{array}{ccccl} D & C & B & A \\ 0 & 0 & 0 & 0 & \rightarrow 0 \\ 0 & 0 & 0 & 1 & \rightarrow 1 \\ 0 & 0 & 1 ...
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  • 68.8k
9 votes

7 segment binary to hex

If you want to fiddle with gates, another possibility is to use a small FPGA or CPLD. You can get started with a flash-based FPGA for a few tens of dollars. Reprogram it as many times as necessary ...
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8 votes

Does my 7 segment display need a bypass capacitor?

A breadboard tends to have high capacitance due to its construction as multiple parallel contacts, and will often act as bypass capacitors for ICs. Transferring to a PCB without adding caps tends to ...
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7 votes

Why does this 7-Segment Display not function properly?

From your table, it's pretty obvious that bit 1 is stuck on. Note that 0000 displays like 0010, 0101 like 0111, etc. This is likely a wiring error, probably a floating input.
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7 votes
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7 segment display not showing digits simultaneously with an ATMega32

That appears to be an LED seven segment display. You can only light up one digit at a time. You have do it one digit after another. If you do that fast enough the digits will appear to all be on at ...
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7 votes
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Using 1N4148 diodes on segments of multiplexed 7-segment LED display

You are correct in looking for the design decisions, and all the information you need is on hand. From your schematic and an assumption that the segment currents are in the 25 mA range we can work out ...
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6 votes
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How to connect 7447 decoder to 7-segment display?

Each segment on a 7-segment display is designated a letter (A-G). This is standard and is shown in the SN7447 datasheet: You can use a diode tester or a simple voltage source and a resistor to ...
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  • 7,450
6 votes
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Possible to use 7447 to drive common-cathode 7 segment display?

Yes, it's possible. One method would be to use two extra resistors (plus the usual per-segment resistor) and one PNP transistor per output. simulate this circuit – Schematic created using ...
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6 votes
Accepted

How to "deserialize" a digital output to 4 digital outputs

You could use a 74HC595 shift register and this circuit, courtesy of Roman Black. That will buy you 8 outputs with a single 25-cent chip.
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6 votes
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Driving large common anode 7 seg LED with NPN transistor and arduino, worked but is it the right way?

Here is a good way to do this: The SEGx lines are 0-5 V digital outputs from your microcontroller. All you need is a single NPN transistor and emitter resistor per segment. The LED current is ...
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6 votes

7 segment binary to hex

But that one only works for BCD (0-9). Actually 7447 physically can accept hex values of A-F, but they display wrong images for them, see here page 3. In my opinion, making hex-to-seven-segment ...
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  • 6,580
6 votes

7 segment binary to hex

MC14495, DM8880/9368, V40511, D345, D346, 4311, 4368 or 74C915 All of these are hard to get your hands on nowadays.
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  • 13.1k
6 votes
Accepted

I am designing a 7 segment display but I am finding it a little bit hard to associate them

The main link for the logic for the individual segments is that they must share the same inputs. Optionally, they can share computation of a given expression: for example, inverted values of all the ...
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  • 2,900
5 votes
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How to drive a single 7 segment display with I2C?

You probably just need a chip like the TCA9554. Connect VCC and GND to digital power and ground, respectively. Connect A0, A1, and A2 to VCC or GND to set the lower 3 bits of the I2C address. Connect ...
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5 votes
Accepted

Why can a 74HC595 drive 8 LEDs?

You can (and should) run the LEDs at lower than the maximum current. Many modern LEDs are plenty bright at a few mA, no need to run them at 20mA unless you are planning to cast shadows across the room ...
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5 votes
Accepted

How to create a short circuit

It shouldn't be necessary to play funny games with resistors and diodes. Lighting LEDs with a microprocessor output is a normal thing to do, and shouldn't require any kind of overly clever circuitry. ...
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5 votes
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Designing a electronic dice with Arduino, 74HC163 and a 74HC4511 decoder to a 7segment display

Overview Essentially, you want a 1-6 counter -- either up or down. So let's go with up. Excitation Table Excitation tables often used to work out the combinatorial logic needed to transition a set of ...
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  • 68.8k
5 votes

The circuit, especially 7 segment parts does not work at all

I see one thing that looks wrong. See the break in the blue line on the breadboard? That means that there is not a connection between that line and where you connected the ground. You have to jumper ...
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5 votes

The circuit, especially 7 segment parts does not work at all

The breadboard power line is physically disconnected between the gaps. Add a jumper cable as indicated in the picture below (red line).
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5 votes
Accepted

How to correctly address this three digit 7-segment display

This task of yours is pretty much MCU-101. Almost everyone who has done anything with an MCU will have tackled this problem early in their learning period. It's classic and dates back 50 years or more....
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  • 68.8k
4 votes
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BCD to 7 Segment Decoder Schematic: Need help fitting in page

This is a question about being artistic I think but, try rotating everything thru 90 degrees or using net-names to connect things to get rid of the main mass of connections. Not sure if you can use ...
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  • 378k
4 votes

How to filter out the mains power supply spikes?

Your 12V linear regulator is most likely running out of headroom, due to the fact that you have a fixed turns-ratio step-down transformer as its input source (which is of course gets rectified and ...
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