How to decode LED display signals?

Discussion in 'Homework Help' started by EI3KI, Jul 6, 2014.

  1. EI3KI

    Thread Starter New Member

    Jul 6, 2014
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    Hello, everybody.
    I get programmable antenna Rotator http://www.ebay.ie/itm/RCA-VH126R-A...177?pt=LH_DefaultDomain_0&hash=item3f2612cdc1 and it’s working perfect with my lightweight 2el 2band Moxon antenna. I have programmed it for every 30 degrees, but I want to put this Control unit in the new box with azimuthal map shown on this box. Have pushbutton switches with LED’s and will put every 30 degrees also. Control unit have keypad switches, but I want to use my new switches with LED included in this switch.
    The keypad have resistance about 60 Ohms between working contacts. Do I need to put resistor in series with new switches, or it will be okay without resistors??? There is AT89951 and 8-th inputs is connected straight to the keypad.
    The number of memory channel is shown on separate 7 segment LED display by some letter (A, b, C, d, E, F, g, H, I, J, U, L). This channel letter is active every time (even after switching off-on). After pushing another memory button, Display starts showing new memory channel Letter and rotator turns. But I don’t want to use this 7 digit LED display, because it’s not informative. More informative will be separate pushbutton switches with LED every 30 degrees around the azimuthal map, because they lights and shows direction. Also there is another double display which shows degrees (decimal) without last third zero, but it’s easy to put this zero. I will use it also.

    The problem is, that I don’t know how to decode every memory channel letter and make to light my pushbutton switch LED. I have tried few variants using AND logic, but my knowledge is not enough. Have browsed internet, but can’t find anything useful (my English is not super also). Maybe somebody can help me and give useful schematic advice, please!

    AT89951 outputs is connected to 3 separate anodes of memory LED display and double degrees LED display using n-p-n transistors. It’s okay, but all 3 the same segment LED’s is connected in parallel and to the same PIC output. I have checked signals on all segments using oscilloscope, but can’t find low or high… there is many impulses and this impulses is changing frequency and polarity while Rotator is working. Too crazy for me…

    If you can help and need more info about this Control unit schematic please ask me. Thanks in advance, EI3KI
     
  2. MrCarlos

    Active Member

    Jan 2, 2010
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    Hello EI3KI

    I do not clearly understand your approach.
    Okay. . . As far as I understand:
    You want to add a new box with azimuth map, among other things.
    I guess at that azimuth map you have 12 points of reference.
    Since you say that: I have it programmed for every 30 degrees.

    I think 4 of those points will be marked as:
    North. South. East. West. On your azimuth map.
    The other remaining 8 points, sure, you're going to bring them some name.

    Making shorter this talk:
    What I understand is that you are requiring assistance to develop a circuit, either, turning the 12 LEDs in the azimuth map, or turn the LEDs on the buttons in your new box.

    Could you explain, please, in other words?
     
  3. EI3KI

    Thread Starter New Member

    Jul 6, 2014
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    Hello, MrCarlos.
    You are right about 12 points around azimuthal map. Existing Control unit have 12 programming memories and they is shown by letters on 7 segment LED display. I must use this Control unit, but need some additional schematic to turn on separate LED's on the buttons together with existing memory channel 7 digit LED display. Display shows some memory and in addition is working separate LED on the memory button.
    Thanks for your answers!
     
  4. EI3KI

    Thread Starter New Member

    Jul 6, 2014
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    Part of Control unit schematic
     
  5. MrCarlos

    Active Member

    Jan 2, 2010
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    Hello EI3KI

    I will assume you want to decode the incoming data to the 7-segment display, so that in the azimuthal map turn on a LED which indicates the orientation of the antenna.

    This is what you intend to do ?

    For the image, Contained in the PDF that you enclose recently, I notice that the figures would be in the 7-segment display of the extreme left.

    That Displays system is multiplexed.
    To synchronize the decoder, you want to do, take the signal arriving at the base of the transistor on the far left.
    when this signal arrives, high level, Take incoming data to 7-Segment Displays.
    These data, with the above said signal, will help us develop the decoder.
    We need to know the name of each line, for each of the segments on the display.

    The decoder will contain the following inputs:
    1 - Strobe.
    2 - 7 signals in the 7-segment display.
    The outputs are 12's which illuminate one of the LED’s on the Map.

    Have you a Software where develop your electronic designs?
     
  6. EI3KI

    Thread Starter New Member

    Jul 6, 2014
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    Hello, MrCarlos.
    I don't have any Software and have never used. I'm soldering some schematic on modeling board, checking how it works and if it suits, I'm making layout and finishing everything. I have some electronic Skills, but not super.

    Do you mean that I need to use 8 input AND logic? 1 input from transistor base and 7 inputs from LED display. But there, to light letter I is 2 LED diodes used only. Another letters is working not with all LED diodes also. Maybe 4 input AND logic with different combinations for every letter displayed? How it's possible to decode this signals? What I can do? Give me some advice, please!
     
  7. MrCarlos

    Active Member

    Jan 2, 2010
    400
    134
    Hello EI3KI

    Take a look at the attached image. (Step 1 Decoder.jpg)

    Through the strobe signal will stored in an IC the content of ones or zeros in the lines that light the segments in the Display.

    The segments are lit in the display according to the letter:
    A Segments a, b​​, c, e, f, g.
    b Segments b c, d, e, f, g.
    C Segments C, d, e, f.
    d segments b, c, d, e, g. . . etc

    We need to adjust the strobe signal because its type is not currently as required.
    The same applies to the signals from the segments.

    Now take a look at the second attached image. (Step 2 Decoder.jpg)
    That way you could go about doing your decoder.
     
    Last edited: Jul 7, 2014
  8. EI3KI

    Thread Starter New Member

    Jul 6, 2014
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    That's great, today I'll order all parts and tomorrow I'll give answer. Thanks, MrCarlos!
     
  9. MrCarlos

    Active Member

    Jan 2, 2010
    400
    134
    Hello EI3KI

    You are one step ahead.
    What parts are you going to order ?

    Remember we have to recondition the strobe signal and the 7 segments.
    The voltage levels where we are taking these signals are very low.
    Or you have already defined the circuits to achieve the purpose?

    Circuits that increase the current voltage to a level compatible to TTL logic circuits are required.

    I think I made a mistake when I defined the segments that go on in the 7-segment display. Take a look please.
     
  10. EI3KI

    Thread Starter New Member

    Jul 6, 2014
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    Hello, MrCarlos.
    I have ordered LS373, LS273 and 12-CD4078. Yesterday have assembled decoder for A and I. There was very low signals on segments and I have used the signals straight from the PIC outputs. This signals is much higher and everything started working. Letter "A" is working okay and only when this memory is enabled. But letter "I" is working all the time, no matter which memory is enabled. Today I will assemble all 12 decoders and will give you full description about all twelve memories. Also the decoder output is not High, but there is high strobe signal on the decoder output pin, which enables to light LED diode not in full.
    See you later
     
  11. EI3KI

    Thread Starter New Member

    Jul 6, 2014
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    Hello again.
    Sorry for long delay, was very busy weekend.
    I have assembled all 12 memory decoders. Results is not good. No matter which memory is turned on, always is light from 6 to 10 LED diodes at the same time.
    I have checked signals on all three transistors (see my schematic) and it seems, that there is the same signal on all three bases always. By my opinion it should be different, because at one moment should be open one transistor only. In next few milliseconds another and so on. When transistor is open, then signals from PIC outputs is turning on Display segments and later the same with second and third transistor.
    What do you think?
     
  12. MrCarlos

    Active Member

    Jan 2, 2010
    400
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    Hello EI3KI

    You need to fix the Strobe signal to a level suitable for the 74LS273.
    Also signals for segments must fix.

    I'm assuming the AT89951 is connected as you look at the PDF I attached.
    The AT89951 is programmed to make high level the strobe signal for the display that must turn on.
    But how high it is ?
    Probably need to measure it, to design a circuit that suits voltage levels for 74LS273.
    Surely the circuit looking into the PDF document serve for that purpose.
    Something similar should be done with the 7 signals for the segments.

    Note that:
    The control signal to your decoder has the name: STB.
    While the output is named Strobe.
    The input signals to your decoder for 7 segments are named by a single vowel.
    While the outputs are double vowel.
     
  13. EI3KI

    Thread Starter New Member

    Jul 6, 2014
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    Hello, MrCarlos
    I did very big job, have measured all Impulses with all possible combinations. Results is attached, I think you will understand it.
    I have increased resistor R11 value to 22k, without increasing Q2 doesn't inverted. Also have increased R9 value to 100k. Pin1 of LS273 to +5. Now everything works better, but:
    After pushing on some memory button light that memory LED and in addition another memory's LED's also. F, I and L is light alone. Below is results
    A + F, H, I
    B + L
    C + L
    D + I, J
    E + C, F, L
    F
    G + I
    H + I
    I
    J + I
    U + I, J, L
    L
     
  14. djsfantasi

    AAC Fanatic!

    Apr 11, 2010
    2,804
    832
    In MrCarlos decoder example in post 7, the output of segment d is not connected to the AND gate. I believe this omission may be the problem. It should be connected to the gate through an inverter (I am not sure of his notation, but if the connected segments are all inverted, then unused segments should be directly connected to the gates.)

    Otherwise, letters which share segments with others, such as I and A, will light together. Only if I is decoded to not include the unused segments will this be correct.
     
  15. MrCarlos

    Active Member

    Jan 2, 2010
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    134
    Hello EI3KI

    You Say:
    Pin1 of LS273 to +5. Now everything works better,
    First of all sorry for My terrible mistake. You are right !
    The 74LS273 PIN 1 must be connected to Vcc. Not grounded.
    Really I’m sorry.

    I checked the .PDF document that you enclose in your post #13.
    I saw the graph for PIN 11 of the 74LS273 is very good. (In the bottom right)
    The low voltage: 0.2, . It's time .8 mS.
    The high voltage: 4.95, It's time 15.1 mS.

    But no so for the signals of the segments.
    You need to build a circuit as you did for the Strobe signal: R9, R10, R11, Q1 and the inverter.
    But now, each of the segments.
    You probably have to change the value of the resistors again.
    Need similar voltage levels that You got in the circuit connected to PIN 11 of the 74LS273.
    Analyzes the circuit contained in the attached image, Voltage Level Adaptor.PNG.

    Now, to analyze the signals from a to g, you have to synchronize your scope to the positive transition of the signal We have called Strobe.
    When this signal is high level (4.95), how or what voltage levels are the signs for each segment ?

    If Our STB signal is high, the transistor conduct current in their joint collector-emitter.
    Therefore the associated Display is forward biased to illuminate the segments having a low level.
    At this very moment. what voltage levels are, in each one of the signals that we name "a" to "g" ?
    There must be a low level (0.2) for segments that should turn on.
    And there must be a high level (4.95) for segments that should not turn on.
    I'm explaining well, you know what I mean ?.

    Now:
    The segments in the Memory Channel Number Display should light according to the letter to display:
    A => a b c e f g.
    B => c d e f g.
    C => a d e f.
    d => b c d e g.
    E => a d e f g.
    F => a e f g.
    g => a b c d f g.
    H => b c e f g.
    I => b c.
    J => b c d e.
    U => b c d e f.
    L => d e f.
    I hope I have not made ​​mistakes.
     
  16. EI3KI

    Thread Starter New Member

    Jul 6, 2014
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    Hello, MrCarlos
    I have not used transistors for inverting the signals of the segments, but have connected in series 2 hex inverters. That's more easy to solder everything. For strobe is used transistor only, because two inverters doesn't work.
    Results is absolutely the same, like in my post #13, except signal levels, which is L=0.2V and H=4.95V. The problem should be in 4078 decoders, because Low and High levels on it's inputs is normal. For letter A = a,b,c e,f,g and so on for all letters. Maybe Mr "djsfantasi" in post #14 is right?
     
  17. MrCarlos

    Active Member

    Jan 2, 2010
    400
    134
    Hello EI3KI.

    You Say:
    The problem should be in 4078 decoders, because Low and High levels on it's inputs is normal.
    The 4078 is not a decoder but a 8 inputs NOR gate.

    One of the things you should do immediately is to check here:
    http://www.alldatasheet.com/
    Inquiring for FULL identification number of 4078. may be MC4078BP.
    Probably the one you have on hands do not work well with 5 volts.
    When you read their datasheets find what bias voltage required to work well.

    If you are using two inverters for the signals of the segments, the voltage at the output of the second inverter must be at least equal to what you get for the Strobe signal; In other words, something must be done to achieve those voltages.

    Now, Let's look to the decoder:

    You'll have a lot of work by the decoder.
    It takes many wires.
    I am attaching some files where you would see how this decoder.
    I just connected the NOR for LED turns on to when the "A" lights on the 7-segment display.

    Also the circuitry for each LED, in PNG format. (The LED Decoder Circuits.ZIP)
    Note that each of these PNG files have inverters, They are not necessary as you can guess by analyzing the image called The Decoder.PNG.
    I'll show only, at that image, the NOR gates that would light the LED’s: A, b, C, d, E, F, and g.
    We would lack NOR gates for LED’s: H, I, J, U and L.
    These circuits, in PNG image format, were made with SoftWare named Boole-Deusto. Excepting the one called The Decoder.PNG.

    Check everything carefully.

    good luck
     
  18. EI3KI

    Thread Starter New Member

    Jul 6, 2014
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    Hi,
    I have used CD4078BM and it's working from 5 to 15 VDD. Min input level should be >3.5V, when VDD is +5. It's everything okay.
    Now I will need few days again, because I don't like thousands of wires on my table and every time I'm making PCB board, except small schematics...:)
    But every day these PCB's become more and more difficult and very soon I will need to make big box for it.:D
    Thanks for your patience and help!
     
  19. MrCarlos

    Active Member

    Jan 2, 2010
    400
    134
    Hello EI3KI

    Well, if you do not want to have many wires you could develop your design with a PIC
    But you you would require more resources:
    1) - Know them to select the most suitable to your design.
    2) - to know some programming language.
    3) - A programmer to program the PIC.
    4) - etc.

    Either way you have to do the: Voltage Level Adaptor. Mentioned above.

    Note:
    Would only be 8 wires for inputs to the PIC coming from the Voltage Level Adaptor circuitry.
    12 outputs wires, in the PIC, to the LED’s output map.
    And of course, 2 wire to polarize the PIC.
    All 1) -, 2) -, 3) - and probably 4) -, are easy to fix.

    In the latter case, someone said:
    You do not need to know everything, what you should keep in mind is to know who can do such a thing and send to do the thing.
    Do not ask me anything about programming. Do not know about that.
    But if you have a friend near you, that know about PICs, can work together to develop your project.
    If he/she has a programmer for PICs ! better !.


     
  20. EI3KI

    Thread Starter New Member

    Jul 6, 2014
    13
    0
    Hi
    The new schematic now contains 21 IC!!!!!!! It's too crazy...:confused:
    I have used PCB design software "Pad2Pad" to create my PCB and it's done. But it's impossible to make this PCB at home and too expensive to order...

    Of your above list I have PIC programmer only...:)
     
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