Dual counter - Page 2 - Electronic Circuits Projects Diagrams Free

Mike, K8LH · 22nd March 2007, 12:11 PM

Gayan, nice video.

bananasiong · 22nd March 2007, 12:17 PM

No, not the real clock, but dual counter. User set the time and then start counting, both are working independently.

bananasiong · 22nd March 2007, 04:37 PM

Hi,
I have done the dual counter, and the result is expected but I need more time to test it.
I don't know why it didn't work previously. I have checked and checked the program, there shouldn't be problem. Just now I deleted all the hex file and recompiled again and load the same program into the PIC again, it worked

Does anyone know how to increase the brightness of the multiplexed 7-segment displays? Can I ignore the collector resistor since there is already base transistor to control the current flow through the collector.

I have almost done my PCB and found that there are 2 extra IO pins. If I need a ground and don't want to route for so long, can I just use the extra pins to make ground (0)?

Thanks

**Nigel Goodwin** · 22nd March 2007, 05:29 PM

Quote:

Originally Posted by bananasiong

Does anyone know how to increase the brightness of the multiplexed 7-segment displays? Can I ignore the collector resistor since there is already base transistor to control the current flow through the collector.

No, you can't ignore the current limiting resistors - the base resistor is nothing to do with it, that's to limit the current from the PIC to the base - the transistors are used as switches, not amplifiers.

If you want to increase the brightness use PNP transistors to feed the segments, with lower value current limiting resistors (modifying the program accordingly). Currently the brightness is limited by what current the PIC can provide.

bananasiong · 22nd March 2007, 05:43 PM

Yes I'm using the PNP transistors.
I thought the collector resistor is to limit the Ic max? As long as the Ic is below Ic max, Ic is controlled by the base current isn't it?

**Nigel Goodwin** · 22nd March 2007, 05:48 PM

Quote:

Originally Posted by bananasiong

Yes I'm using the PNP transistors.

Sorry, the diagram is on another page - I meant NPN, as well as the PNP.

Quote:

I thought the collector resistor is to limit the Ic max? As long as the Ic is below Ic max, Ic is controlled by the base current isn't it?

Only if you're using the transistor as an amplifier and not a switch - add NPN's and lower the resistors - all removing the resistors would do is strain the PIC.

Mike, K8LH · 22nd March 2007, 05:58 PM

You could also use a ULN2003 (or ULN2803) sinking driver IC instead of seven NPN transistors.

bananasiong · 22nd March 2007, 06:02 PM

Okay, luckily I didn't remove the resistors.

Can I know what is Code protection (CP & CPD) for the fuse setting? And what's about Power up timer reset?

I've read the datasheet of 16F877A, it shows that there are 15 interrupts, what's the purpose for having more than one interrupt? How does it work?

bananasiong · 22nd March 2007, 06:08 PM

Quote:

Originally Posted by Mike, K8LH

You could also use a ULN2003 (or ULN2803) sinking driver IC instead of seven NPN transistors.

Why is it needed? Direct from the output pin to the base via a resistor will do right?

Mike, K8LH · 22nd March 2007, 06:12 PM

I was supplementing Nigel's suggestion of using NPN segment driver transistors to improve overall display brightness.

bananasiong · 23rd March 2007, 01:13 AM

Use PNP as 7-segment display selection and NPN for the patterns right?
I think I will just reduce the resistance of the collector, because the PCB space is limited.

**Nigel Goodwin** · 23rd March 2007, 08:37 AM

Quote:

Originally Posted by bananasiong

Use PNP as 7-segment display selection and NPN for the patterns right?
I think I will just reduce the resistance of the collector, because the PCB space is limited.

But the PIC hasn't got enough current capability - which is why the resistors are there! - check the PIC datasheet, maximum current per pin, and maximum total current.

eblc1388 · 23rd March 2007, 09:54 AM

Quote:

Originally Posted by bananasiong

I've read the datasheet of 16F877A, it shows that there are 15 interrupts, what's the purpose for having more than one interrupt? How does it work?

The purpose is to allow user to process up to 15 different requests, which user has no idea when they will happen in real time but need to service them none the less, and not wishing to test them one by one in an endless loop wasting processor power. In PIC 16F families, all interrupt requests, if enable by the user, would jump to address location 0x0004 regardless.

It is up to user to test for what type of interrupt are requested and then branch to the correct service routine inside the interrupt handler.

In case of AVR, the interrupt is vectored, so different request would jump to different fixed address locations in which user can place the correct jump address for the required handler.

bananasiong · 23rd March 2007, 10:12 AM

Yes, I know that only 25 mA for every pin, sinking and sourcing.

Thanks

gramo · 23rd March 2007, 11:45 AM

My 2 bob on this thread, given its already evolved quite far, use the UL2003 and Common Cathode 7-Segment displays.

This way you can ditch the resistors on the base of each transistor and directly control the switching via the ULN2003, reducing external components from 8 to 1 for your multiplexing.

The ULN2003 acts like an "earth" switch, eg, a high on the input from the PIC will switch the output to earth

This is great for devices that use up to 500mA!

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22nd March 2007, 12:11 PM	(permalink)
Mike, K8LH	Gayan, nice video.

22nd March 2007, 12:17 PM	(permalink)
bananasiong	No, not the real clock, but dual counter. User set the time and then start counting, both are working independently. __________________ Superman returns..

22nd March 2007, 04:37 PM	(permalink)
bananasiong	Hi, I have done the dual counter, and the result is expected but I need more time to test it. I don't know why it didn't work previously. I have checked and checked the program, there shouldn't be problem. Just now I deleted all the hex file and recompiled again and load the same program into the PIC again, it worked Does anyone know how to increase the brightness of the multiplexed 7-segment displays? Can I ignore the collector resistor since there is already base transistor to control the current flow through the collector. I have almost done my PCB and found that there are 2 extra IO pins. If I need a ground and don't want to route for so long, can I just use the extra pins to make ground (0)? Thanks __________________ Superman returns..

22nd March 2007, 05:43 PM	(permalink)
bananasiong	Yes I'm using the PNP transistors. I thought the collector resistor is to limit the Ic max? As long as the Ic is below Ic max, Ic is controlled by the base current isn't it? __________________ Superman returns..

22nd March 2007, 06:02 PM	(permalink)
bananasiong	Okay, luckily I didn't remove the resistors. Can I know what is Code protection (CP & CPD) for the fuse setting? And what's about Power up timer reset? I've read the datasheet of 16F877A, it shows that there are 15 interrupts, what's the purpose for having more than one interrupt? How does it work? __________________ Superman returns..

22nd March 2007, 06:12 PM	(permalink)
Mike, K8LH	I was supplementing Nigel's suggestion of using NPN segment driver transistors to improve overall display brightness.

23rd March 2007, 01:13 AM	(permalink)
bananasiong	Use PNP as 7-segment display selection and NPN for the patterns right? I think I will just reduce the resistance of the collector, because the PCB space is limited. __________________ Superman returns..

23rd March 2007, 10:12 AM	(permalink)
bananasiong	Yes, I know that only 25 mA for every pin, sinking and sourcing. Thanks __________________ Superman returns..

23rd March 2007, 11:45 AM	(permalink)
gramo	My 2 bob on this thread, given its already evolved quite far, use the UL2003 and Common Cathode 7-Segment displays. This way you can ditch the resistors on the base of each transistor and directly control the switching via the ULN2003, reducing external components from 8 to 1 for your multiplexing. The ULN2003 acts like an "earth" switch, eg, a high on the input from the PIC will switch the output to earth This is great for devices that use up to 500mA! __________________ Spency. PIC Micro's - Your mind is the limit PIC's and interfacing with other devices - a PIC Basic Guide @ digital-diy.net