48

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 mean that you are currently pushing 172 milliamps, or almost 3 watts through your resistor. If that is the case, you should lower your power supply to less than ...


39

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 the segment. Where you've gone wrong is assuming there's 6.8V forward voltage drop per LED. There is no such red LED. Typically a red LED will be around 1.6V-...


29

Yes, it sounds like you are seeing artifacts of toothbrush frequency vibrating your head and therefore your eyes, and that beating against the LED refresh frequency. This is a similar effect to eating potato chips (actually anything crunchy) while watching the LED display. In that case the head vibrations are more random, so parts of the LED display will ...


28

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 and resemble print typeface numerals more closely. The others look like italics which we are used to reading and the eye seems to accommodate this quite ...


26

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's some discussion of that over here. What's missing from that discussion is that a slight rightward slant gives characters that are slightly more similar to ...


19

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". These days LED's are very efficient. They no longer need the 20mA the first generation required. 1mA or less is not uncommon. So, yes, you drive these straight ...


16

The two schematics are two versions of the display, common cathode at the top, common anode at the bottom. I'll assume you have the common cathode version. You connect the segments A..G, DP via 8 series resistors to 8 I/O pins of the microcontroller. Driving a pin high will light that LED on the selected digit. To select any of the 4 digits you make the ...


16

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 late 1980s and beyond.


12

LCD display without back-light is the only possible solution on these conditions. Something like this: Here is some example data sheet: Link to PDF


11

It looks OK, but the resistors should go on the cathode side. With the resistors on the anode side your display will change in brightness depending on the number of LEDs which are on. A "1" will appear brighter than an "8". Also keep in mind that the TLC59213 is a registered device: you'll have to latch the data on the inputs to the actual driver with a ...


11

The purpose of the resistor is to limit current to a segment LED, by dropping the surplus voltage (over the LED Vf) across itself. When a resistor is used on a common cathode, the current through this resistor would vary by the number of segments lit at any time. Thus, the voltage dropped would change as well. This will lead to intensity of digits changing ...


11

The Double-dabble technique converts binary to BCD by repeated shifting. Each repetition halves the remaining binary number and doubles the BCD number, after the complete binary value is shifted the result is obtained. After each shift a correction is applied to each 4-bit BCD column (or those having more than 3 bits shifted in by that point). This ...


11

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 contraption; If you happen to use some highish efficiency LED displays, you may even be able to drive a common anode one directly. The '!EN' pin can be either of the ...


10

Life can be tough. CMOS ICs from the CD4000 series, like the CD4026 can only source and sink very little current, typically 1 mA at 5 V and that will be much too little for a typical 7-segments display. So I'm afraid you'll need the transistors, especially since you're now already asking for more brightness. But You don't necessarily need all these ...


9

The cheapest solution may be a microcontroller programmed for that purpose. This is all you need: displays, a couple transistors and resistors. Should be possible for about $2. If you really want to control the colon you need a fifth transistor. (If it's always on you can leave it out of the microcontroller's way, and simply connect current-limiting ...


9

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 & 0 & \rightarrow 2 \\ 0 & 0 & 1 & 1 & \rightarrow 3 \\ 0 & 1 & 0 & 0 & \rightarrow 4 \\ 0 & 1 & 0 & 1 &...


9

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 to get it right, and you generally get a lot of I/O pins per dollar. Example VHDL code here For example, (shaky and not quite a complete loop, but you get the ...


8

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 leave some designs not working. That said, the 7 segment display is just bare leds, and those do not need a bypass capacitor. The ICs you are using will. 0.1 µF ...


7

Actually this is a very common arrangement. Each digit has its anodes connected together, and the segments for all digits have their cathodes connected. The controller enables one of the common anodes, drives the segments, and waits, then turns off the cathodes and moves on to the next common anode. This arrangement and control method is called multiplexing, ...


7

Two obvious possibilities come to mind: You messed up the stripboard wiring. There is not much more we can help with that. You say there are over 100 wires, so the chance of a screwup, and then not catching it, is high. A real circuit board is the obvious solution. Your design left something floating, and it happened to work on the breadboard. Perhaps ...


7

Get a power source (5 .. 12V DC) and connect a 1k resistor to the +. With the two wires, connected to gound and the (other side of) the resistor you can probe various pin combinations. When you have a combination that lights up a segment, start trying other pins while holding one pin fixed. These are LED displays, so they are direction sensitive. In most ...


7

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.


6

First, you shouldn't place the resistor on the ground side, but one at each output of the LS164. To get 20mA the value should be 150\$\Omega\$. Next, the LS164 is a bad choice. You want a latched shift register, where you can freely shift data without disturbing the outputs. The TPIC6C595 is compatible with the often (ab)used 74HC595, but the latter can'...


6

Do not upvote this answer! Blake found the solution himself, but doesn't seem keen on posting it as an answer. I'm just posting as a Wise Lesson for Future Generations. Driving the common anodes directly he made one output high at a time, and the outputs for the not selected displays low. But adding the PNP transistors inverses the logic, and then you ...


6

Price point is something you'll be hard-pressed to negotiate without serious volume. If the price is not something that can slide, you're likely to be stuck buying raw panels and adding the controller ICs / communication ICs to a custom designed board. If you can let the price slide, there are some nice pre-made modules you could look into. Adafruit has "...


6

6-digit 7-segment displays are not very common: Single, 2, 3 and 4 digit modules are much more easily sourced. Here is one 6-digit 7-segment intelligent display module that can be bought as a kit or fully built - it actually consists of two 3-digit displays on a single PCB, with a serial interface: It uses a serial input, 9600 baud, 8 data bits, 1 start ...


6

My first assumption from the symptom is that you have a single cathode resistor, which would explain everything. However, you say this is not the case and that you have individual 100 Ω resistors on each anode line. The answer then must be that whatever is driving the cathode can't handle the combined current. Apparently you are driving the cathode ...


6

If the drivers for the original LEDs can supply enough current you can do this with a diode matrix: route the current from each of the original LEDs to the segments you want to illuminate when that LED would have been on. In my experience a high-brightness display will be OK with ~ 1 mA per segment. Details will depend on exactly how the current LEDs are ...


6

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.


6

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 determine the pinout of your particular display. Then just map the pins correctly (again, from datasheet):


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