Peripheral Devices That I have but Don't know how to use. Help Please.

Adding to the list of Devices that I can't use is an IC 7 Segment display Decoder (http://www.jaycar.com.au/products_uploaded/ZC4511.pdf).  I can wire the corresponding letters to the corresponding segments but I don't understand what some of the pins are:

1. LE

2. LT

3. BT

On the Display itself, it has a pin marked Dp which I guess is the backlight.  Where does this go on the IC?

And it is a Common Cathode Display (I checked).

Thanks in advance.

Fergus Byrne wrote:

 

Adding to the list of Devices that I can't use is an IC 7 Segment display Decoder (http://www.jaycar.com.au/products_uploaded/ZC4511.pdf).  I can wire the corresponding letters to the corresponding segments but I don't understand what some of the pins are:

1. LE

2. LT

3. BT

 

 

On the Display itself, it has a pin marked Dp which I guess is the backlight.  Where does this go on the IC?

 

And it is a Common Cathode Display (I checked).

 

Thanks in advance.

The CD4511 data sheet describes ~LT, ~Bl, and LE in text and in the truth table.  ~LT is "Lamp Test" and when low turns on all segments.  ~LT has priority over all other inputs.  ~Bl is "Blanking" and when low turns all segments off, assuming ~LT is high = inactive.  ~Bl is used to blank the display to save power or can control brightness using pulse width modulation, i.e., with a variable duty cycle.  It has priority over LE.  LE is "Latch Enable" and when high stores the DCBA input that was present when LE rose from 0 to 1.  If LE = 0, the latch is transparent and segments a-g follow DCBA.  If LE = 1, the CD4511 ignores the DCBA inputs and displays the stored DCBA value.  LE is useful if you want to drive multiple digits from RasPi's limited GPIO signals since you can share the DCBA signals and provide a separate LE for each digit.

CD4511 a-g outputs are active high and need to be used with a common cathode LED array.

The decimal point DP is not controlled by the CD4511 and if used must be driven with other circuits.

So, When connecting it to the RPi, I have to connect the A, B, C, D to GPIO pins and go high when I want then 'on'.

The Vss is the ground on the chip?

the Vdd is the 5v power on the chip?

The DP to the 5 volt circuit?

Common Cathodes (two of) to Ground?

And ignore the other inputs and outputs (LT, LE, Bl)?

Fergus Byrne wrote:

 

So, When connecting it to the RPi, I have to connect the A, B, C, D to GPIO pins and go high when I want then 'on'.

 

The Vss is the ground on the chip?

 

the Vdd is the 5v power on the chip?

 

The DP to the 5 volt circuit?

 

Common Cathodes (two of) to Ground?

 

And ignore the other inputs and outputs (LT, LE, Bl)?

The CD4511 (according to your link to Fairchild Semi data sheet) is a CMOS part with CMOS input voltages.  VSS is ground.  VDD is the supply, which can be anywhere from 3V to 15V.  In your case you probably want to use +3.3V for VDD.  The reason is that CMOS input voltage thresholds for logic 1 (high) and logic 0 (low) vary with the supply voltage, i.e., anything below 30% of VDD is logic 0 and anything above 70% of VDD is logic 1.  Input voltages in the middle are not valid and may cause the CMOS part to use excessive power.  While you can drive a 5V CMOS input from RasPi's 3.3V GPIO outputs without damaging anything, it's not a good idea because 70% of 5.0V is 3.5V so the highest voltage RasPi can produce is not a valid logic 1.

Another thing with CMOS inputs is that you must connect them to a valid logic 1 or 0 -- do not leave them floating.  In your case, pull up the ~LT and ~Bl signals with a 4.7K or 10K Ohm resistor (safest), or tie them directly to VDD (should work, but I prefer the resistor).

If you only want to drive a single digit, tie LE to 0 = GND.  This will cause segments a-g to follow BCD code DCBA continuously.  Just drive DCBA with your RasPi and the CD4511 will happily display the digit.

If you want to drive multiple digits, tie each digit's LE to a RasPi GPIO and tie all the DCBA signals together.  Then have your software set DCBA to the value for a digit and toggle its LE from low to high to update one digit at a time.

RasPi's 3.3V GPIO pin is limited to 50 mA.  This is enough to drive 16 LED segments if each is 3 mA.  The CD4511 itself uses far less than 1 mA.  If you want more segments or have higher currents, you'll need to add a separate voltage regulator to generate VDD from 5V.  A quick-and-dirty one is to use a silicon diode plus a pull-down resistor (1K is good), which will drop 0.6 to 0.7V resulting in VDD = 4.3 to 4.4V.  This will give you a CMOS input threshold of 3.08V or lower, which will allow RasPi to talk to the CD4511.

The common LED cathodes all go to ground.  Each LED anode needs it own resistor between the CD4511 output and the LED array input.  To calculate the resistor value, first figure out how much current each LED needs (typically 3 mA for modern high-efficiency LEDs, or 10-20 mA for the 1970s vintage LEDs I have in my parts cabinet).  The voltage drop across an LED depends on its color, typically 1.6V for red, 2.1V for yellow, or 2.4V for green.  You can measure these with a multimeter.  According to the CD4511 data sheet, each output pulls up to about VDD-0.7V at 3 mA.  So the voltage drop across the resistor for a yellow LED is about VDD-0.7V-2.1V = VDD-2.8V.  So for VDD=3.3V, you have a 0.5V drop across the resistor.  At 3mA, you need a 500mV/3mA = 160 Ohm resistor.

If the decimal point LED is 3 mA, you can drive it from RasPi through a resistor.  RasPi probably pulls up to 3.0V, so with a yellow LED the drop across the resistor is 3.0V-2.1V = 0.9V.  At 3 mA you need a 900mV/3mA = 300 Ohm resistor.

I have now wired the chip as per the specifications above ^.

Can someone please check my code and tell me why it won't work please.

import RPi.GPIO as GPIO

GPIO.setmode(GPIO.BOARD)

GPIO.setup(7, GPIO.OUT)

GPIO.setup(11, GPIO.OUT)

GPIO.setup(12, GPIO.OUT)

GPIO.setup(13, GPIO.OUT)

 

 

# 7 = Decoder A   2^0 = 1

# 11 = Decoder B  2^1 = 2

# 12 = Decoder C  2^2 = 4

# 13 = Decoder D  2^3 = 8

 

 

i = input("Enter the Number 0 - 9: ")

while i!="":

          if i=="0":

                    GPIO.output(7, GPIO.HIGH)

                    GPIO.output(11, GPIO.HIGH)

                    GPIO.output(12, GPIO.HIGH)

                    GPIO.output(13, GPIO.HIGH)

          elif i=="1":

                    GPIO.output(7, GPIO.LOW)

                    GPIO.output(11, GPIO.HIGH)

                    GPIO.output(12, GPIO.HIGH)

                    GPIO.output(13, GPIO.HIGH)

          elif i=="2":

                    GPIO.output(7, GPIO.HIGH)

                    GPIO.output(11, GPIO.LOW)

                    GPIO.output(12, GPIO.HIGH)

                    GPIO.output(13, GPIO.LOW)

          elif i=="3":

                    GPIO.output(7, GPIO.LOW)

                    GPIO.output(11, GPIO.HIGH)

                    GPIO.output(12, GPIO.HIGH)

                    GPIO.output(13, GPIO.HIGH)

          elif i=="4":

                    GPIO.output(7, GPIO.HIGH)

                    GPIO.output(11, GPIO.HIGH)

                    GPIO.output(12, GPIO.LOW)

                    GPIO.output(13, GPIO.HIGH)

          elif i=="5":

                    GPIO.output(7, GPIO.LOW)

                    GPIO.output(11, GPIO.HIGH)

                    GPIO.output(12, GPIO.LOW)

                    GPIO.output(13, GPIO.HIGH)

          elif i=="6":

                    GPIO.output(7, GPIO.HIGH)

                    GPIO.output(11, GPIO.LOW)

                    GPIO.output(12, GPIO.LOW)

                    GPIO.output(13, GPIO.HIGH)

          elif i=="7":

                    GPIO.output(7, GPIO.LOW)

                    GPIO.output(11, GPIO.LOW)

                    GPIO.output(12, GPIO.LOW)

                    GPIO.output(13, GPIO.HIGH)

          elif i=="8":

                    GPIO.output(7, GPIO.HIGH)

                    GPIO.output(11, GPIO.HIGH)

                    GPIO.output(12, GPIO.HIGH)

                    GPIO.output(13, GPIO.LOW)

          elif i=="9":

                    GPIO.output(7, GPIO.LOW)

                    GPIO.output(11, GPIO.HIGH)

                    GPIO.output(12, GPIO.HIGH)

                    GPIO.output(13, GPIO.LOW)

          else:

                    print "You didn't enter a valid number!"

 

          i = input("Enter the Number 0 - 9: ")

if: i == "":

          print "Closing application..."

It just skips to the else statement with in the while statement. here the statements are not nested but in my code, they are nested.

Bit of a mess but here is a schematic of what I have wired up.  Last night, I had power going into the DP and a little light came on but today that is not happening.  Have I blown the chip?

Bit of a mess but here is a schematic of what I have wired up.  Last night, I had power going into the DP and a little light came on but today that is not happening.  Have I blown the chip?

Fergus Byrne wrote:

 

Bit of a mess but here is a schematic of what I have wired up.  Last night, I had power going into the DP and a little light came on but today that is not happening.  Have I blown the chip?

I don't see any current limiting resistors in your diagram.  Typical LEDs use 1.6V (red) to 2.4V (green).  If you put 3.3V across them without current limiting they will emit a lot of light -- once.  Then they'll be DED.  Driving one directly from a RasPi BCM2835 output without current limit could also damage the BCM2835 output.

I just checked Wikipedia.  They have a thorough article on LEDs and also one that shows how to power an LED using a current limiting resistor and how to calculate its value.  Typical values are 150 Ohm to 1K Ohm depending on the driver voltage, the LED's efficiency and how bright you want it to be.

So you think I have "blown the bolb" on the 7 segment display?  If so, that would mean that the IC is still in place and I can get up and running when I get a new 7 segment dispaly...Right?

Fergus Byrne wrote:

 

So you think I have "blown the bolb" on the 7 segment display?  If so, that would mean that the IC is still in place and I can get up and running when I get a new 7 segment dispaly...Right?

You've probably only destroyed the DP LED.  If you didn't see a bright flash from the other segments, they're probably still intact.  It all depends on what the CD4511 DCBA inputs were when you powered it on.  If DCBA are 1010 through 1111 then outputs a-g are low and the LEDs aren't driven.  With the CD4511 disconnected, try powerering each LED segment from +3.3V through a 150-300 Ohm resistor and see which ones still light up.

You could test your display by using the diode test setting on a multimeter.

If your meter is digital, the negative lead goes to the CC connection and then one by one place the positive lead on the segment pins, each segment will light. Possibly very faintly, depends on the actual display involved.

If your meter is an analogue one (it has a needle meter), then you might need to reverse the connections above. The meter is unlikely to give more than 2v and will be low current.

Will look into it when I get back from holidays.  Thanks for responce.