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Need help with DC Dimming seven seg displays.

AnalogKid

Jun 10, 2015
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Upon re-reading 13 and 15 ... A little projection crept into my response, which was targeted more at my assumption about the circuit's intent than directly at ratstar's post. His circuit description is indeed correct. oops.

The site won't let me edit #15.

ak
 

Schematicsman

Feb 14, 2018
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Hi, everyone sorry I haven't written anything back as I have been unwell for sometime but all good now .
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Intensions:
I'm trying to Learn how design a complete device that will interface and power the complete circuit from RS232 port with regulated voltage of between 5 to 12V dc. I'm using 5 x Common Anode 7 segment displays with transistors ,also using standard LDR like in the pic below to control the brightness off the displays and Pot described below :eg displays should dim when day and full brightness at night , there will also be 3 x DPDT MOM OFF MOM toggle switches to increment or decrement each digits.
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Parts List:
1 x PIC16F628A for the control of most of circuit.
5 x Common Anode Displays Multiplexed and need FULL Brightness maxed out.
5 x BC557A Transistors
1 x RS232 Converter to TTL Module .
1 x On/Off /Vol /Pull to Test Potentiometer
Sorry for the mouth full guys, I hope I'm making sense. any help is appreciated
 

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Harald Kapp

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I'm trying to Learn how design a complete device that will interface and power the complete circuit from RS232 port with regulated voltage of between 5 to 12V dc.
A standard RS-232 port will not be able to deliver the supply power you need for 5 7-segment digits. You'll have to supply the power separately.
Why do you use a RS-232 port at all? You mention buttons/switches to increment or decrement the digits. How are you going to control 5 digits by 3 switches? Is that to be done in software? So where's the need for the RS-232 port?

As stated in the previous responses your circuit will not work - correct setups have been provided. Please post an updated schematic of your circuit.

Dimming can be provided by software, too. You'll have to:
  1. Use the LDF in a voltage divider setup and feed the light dependent voltage to an ADC input of the PIC. Read the analog voltage and adjust brightness accordingly (see 2.) Here is how it is done.
  2. Use the PIC to multiplex the 7-segment display By adjusting the duty cycle (ratio of on time to off time) you can adjust the brightness. Here is how it is done.

What is the potentiometer to be used for if the brightness is being controlled by the LDR?
 

Schematicsman

Feb 14, 2018
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Thanks for the reply guys . I’m wanting to build a radio navigation aid to interface to flight sim software through rs232.

Now the sw1 | sw2 |sw3 toggles with increment or decrement each of the last 3 digits from the 5. Sorry my mistake your right, the potentiometer will be on off /vol Only And not for led brightness. And also what kind of extra circuit is needed to be able to power the whole unit from rs232?
 

Harald Kapp

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And also what kind of extra circuit is needed to be able to power the whole unit from rs232?
This is not possible. RS-232 is a data interface, not a power interface. You'll need a separate power supply.
 
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