7 segments display

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7 segments display

Postby APAK » Mon Jun 13, 2011 8:24 am

Guys ,

How I connect physically 7 segments display to use them with LED64-Advanced ?

Thanks and Regards

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Joined: Sat Nov 12, 2011 6:44 pm

Re: 7 segments display

Postby hammerstan » Sun Nov 13, 2011 4:44 am


• Create a 5 digit display using a single multiplexed 7 segment LED display and minimal electronic components
• I haven’t studied electronics therefore I’ve found using IC/chips based methods overly complex
• Instead I simply wire a 5 digit 7 segment LED directly to a Phidget LED 64 board, via 5 PNP transistors
• The same technique can be used to program 2, 3 or 4 displays (single displays don’t need the transistor and can be wired directly to the Phidget board)

• Benefits - Significantly reduces the number of Phidget slots for a 5 digit display vs traditional method of wiring a collection of single digit LEDs each using up to 8 Phidget slots (ie only 13 vs 5*8=40 for a 5 digit LED display)

• Negatives (I would welcome any suggestions to resolve these issues)

- Requires programming (I use VB6) with an interval of <30ms between illuminating each digit (ie activating its respective diode). However the VB6 Timer object cannot handle intervals of <30ms . Consequently I’ve had to resort to a “for i=0 to 6000” loop to create a delay counter, which while works, is very CPU intensive and hogs program control. Any suggestions on a better way is very welcome

- Even with this method there is some unacceptable flickering. Shortening the interval too far results in the system breaking down. Any suggestions?

What you need
• Phidget LED 64 board (http://www.phidgets.com)
• a common anode 5 digit multiplexed 7 segment LED
• 5x PNP transistors (I used a Fairchild PN 3638A)
• Knowledge of how to program the Phidget board – very easy using Visual Basic based on instructions provided by Phidget, which are excellent boards for many applications

Circuit Diagram - Refer attached file
(Note: If someone can advise whether I have labelled the B, C, & E correctly for a PNP transistor & not around the wrong way)

How To

1. Choose a common Phidget anode rail
- The Phidget LED 64 have two common anodes
- One for the even numbered connector slots (ie 0 to 62), and one for the odd numbered connector slots (1 to 63)
- Choose to use either the even or odd sockets (don’t mix)

2. Wire the LED display common cathodes A to G & DP
- Connect Cathodes A to G and the decimal point (DP) on the 7 segment LED display to 8 black wires (cathodes) connected into the odd or even sockets on the Phidget board (examples uses even slots):

LED Display Cathode - Phidget Connector Slot (black wire only)
A - 0
B - 2
C - 4
D - 6
E - 8
F - 10
G - 12
DP - 14

- The red (anode) Phidget wire is not used
- Turning any of these Phidget slots on will control each of the 7 segments for the active digit (the active digit is controlled via step 4 below)

3. Wire the LED common anode for digits 1 to 5
- Connect the common anodes for digit 1 on the 7 segment display to the right leg of the transistor (that is right leg while holding the flat face of the transistor away from you) – I think this is the transistor “Collector”
- Repeat for digits 2 to 5 using the remaining transistors

4. Connect the transistors to the Phidget
- Using additional Phidget connector slots, wire the black & red wires from each Phidget slot to the other 2 legs on each transistor
- Red wire (common anode) onto the left leg (while holding the flat face of the transistor away from you) – transistor “Emitter”
- Black wire (cathode) onto the centre leg - transistor “Base”

LED Display Common Anode - Phidget Connector Slot (black & red wire)
Digit 1 - 16
Digit 2 - 18
Digit 3 - 20
Digit 4 - 22
Digit 5 - 24

- Turning any of these Phidget slots on will active the respective digit
- Note that the Phidget instructions suggest the Phidget cannot control a transistor – well it appears it can (using off label!)

5. Programming
- This set up wires 5 digits, or 40 individual LEDs using only 12 Phidget connector slots, the alternatively would be to use 40 connector slots
- The drawback is only one digit can be displayed at a time, necessitating a small interval <30ms between illuminating each digit
- Therefore the program running the Phidget must cycle through activating Digits 1 – 5 rapidly for the eye to see all 5 digits active – I’ve used a “for i=0 to 6000” loop to create a delay counter to achieve a delay of <30ms (The counter counts to 6000, but VB6’s Timer object can’t tell me what the actual time delay is given VB6 is not accurate to <30ms)
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