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pasicr
Joined: 13 Aug 2005
Posts: 249
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 02 Feb 2008 15:48 Replace TPIC6B595 with 74HC595 + ULN2803 |
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Hi for all,
Am I thinking proprly?,
I can't find in my country TPIC6B595, this is ser in to par. out shift register for high current application,
can I substitute TPIC6B595 with 74HC595 + ULN2803,
best regards
p.s. I need this for that project
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FvM
Joined: 22 Jan 2008
Posts: 1825
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Location: Bochum, Germany
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| 02 Feb 2008 16:21 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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Hello,
also if the TPIC is available, the two-IC variant could be meaningful in cost-sensitive applications or if you want to be flexible inprocurement. However, TPIC DMOS outputs have better performance in some regard than 2803 bipolar darlington, e. g. lower voltage drop and higher switching speed.
At the serial interface, both solutions are equivalent.
Regards,
Frank
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pasicr
Joined: 13 Aug 2005
Posts: 249
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| 02 Feb 2008 16:40 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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Thanks FvM,
regards
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melc
Joined: 08 Apr 2005
Posts: 386
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| 02 Feb 2008 17:40 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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There is a simpler way to connect four giant LED's to a microcontroller. It's called multiplexing.
Take a look here, it's a clock not a thermometer but there left unused pins for 1wire bus (RB7):
http://www.geocities.com/vsurducan/electro/PIC/two.html#clock
You will need just one driver instead of four.
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Alan69
Joined: 01 Apr 2005
Posts: 76
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| 05 Feb 2008 8:25 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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This is latched, not scanned, and there are some benefits.
For OP, allegro etc 5895 is a very similar part, basically 595 with driver outputs, maybe different pinout though. Also likely hard to find, but another part number someone may have near you..
Also remember that you can use penny transistors. A regular 595 and small transistors on each output works fine, and if you are making a board etc they really don't take much space with a tight pattern beside the output. Since you already need a resistor for the LED segments, make sure you get PNP or NPN to match your display (as in common anode or cathode) so you can use an emitter follower. Basically this just duplicates the transistors inside a simple driver chip, sometimes 32 small transistors is actually easier to deal with than the driver IC. Plus it's easily scalable, you can put large transistors for heavy current much easier/cheaper than you can get a large current driver chip..
Also, another alternative for drivers is ACT. 74ACT series 8 of buffer chips (like 74ACT541 etc) can put out some good currents, like tens of mA. Really some of them are capable of doing hundreds of mA without much problem, depends on how important the project is to not ever fail for how far you push them. You have to check though, they are sometimes more expensive than the cheap 2803s etc, depends on the deal you can find..
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blueroomelectronics
Joined: 17 Sep 2006
Posts: 1140
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Location: Toronto, Canada
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| 05 Feb 2008 15:54 Replace TPIC6B595 with 74HC595 + ULN2803 |
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It's generally poor design to use a low I/O micro and a lot of expensive glue logic when a micro with more I/O would eliminate the glue logic.
To run 4 seven segment displays takes only 11 I/O pins and 4 transistors so why not use a bigger micro?
If you are really cramped for I/O you could also do it with a CD4511 and 4 transistors 8 I/O pins.
Cricket Thermostat prototype
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Alan69
Joined: 01 Apr 2005
Posts: 76
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| 11 Feb 2008 22:00 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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| blueroomelectronics wrote: |
It's generally poor design to use a low I/O micro and a lot of expensive glue logic when a micro with more I/O would eliminate the glue logic.
To run 4 seven segment displays takes only 11 I/O pins and 4 transistors so why not use a bigger micro?
If you are really cramped for I/O you could also do it with a CD4511 and 4 transistors 8 I/O pins.
Cricket Thermostat prototype |
LOL, that's like saying you should only cook eggs by the dozen. Fine if you only want to stuff yourself with eggs every morning, but silly for most anyone wanting to have a few eggs.
That's multiplexed, and there are good reasons to use directly driven in many cases.
Most any commercial design for a 1 or 2 line message center uses exactly these for totally different reasons than you'll think of. Just because you like one way, and aren't familiar with where and when the design should change over, doesn't mean it isn't valid.. Your thinking will tie up 11 pins to save only a little on glue, and require constant scanning. There are plenty of reasons to switch over to a latched design when it makes sense.
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Sinisa
Joined: 03 Mar 2003
Posts: 209
Helped: 38
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| 12 Feb 2008 22:44 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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| I agree Alan69. For most project involving LED display I use same solution logic with CMOS shift register. I have pre-made PCB with 8 digits that I break away as many digits as I need. Small number of wires if display is not at the same place as micro, no scanning and quick implentation.
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blueroomelectronics
Joined: 17 Sep 2006
Posts: 1140
Helped: 54
Location: Toronto, Canada
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| 13 Feb 2008 8:07 Replace TPIC6B595 with 74HC595 + ULN2803 |
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Yes the 74xx595 and ULN2803A work well, a simple 3 wire interface is all you need. But now you have 8 additional ICs.
Muxing a display is not that tough, after all it's running on a microcontroller. It's generally easier than the I2C routines too bad the 16F628 doesn't have a hardware MSSP (I2C, SPI), do you think the 1wire routines are easy?
The LCD display on the 16F917 is dirt easy and it's all done automatically in hardware. Zero software overhead.
Notes:
1. four seven segment displays will put out enough heat to throw off the DS1820 if it's on the same PCB.
2. Use a big PIC like the 16F877A, it has enough I/O to drive four displays with zero glue logic and hardware I2C plus debug support.
3. 2.3" (2 LED) displays can be run on 5V the 12V with 220ohm resistors seems a bit extreme and probably for 4" (5 LED) displays.
Below is a kit I sell called Dragonfly
Six Seven Segment displays can be built with dual colons HH:MM:SS
DS1820 support
Six button keypad
RS485 option
32.768kHz watch crystal timebase for accurate timekeeping
USER I/O Expansion
The Dragonfly digital display
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Alan69
Joined: 01 Apr 2005
Posts: 76
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| 13 Feb 2008 17:28 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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Yep, and most long x8 or x16 displays use these. You feed in a long chain of data then latch, and then turn on a power transistor to light the entire row. Since most of these type chips are latched, you can be feeding new data for the next row while the last row is being lit.
Most large message centers (with the real light bulbs and triacs driving them) also use these. Usually 8, one for each row on that 8x8 grid. Data comes in one side, through that driver, and out the other side into the next driver. So essentially like the above long chains for a row, but you have one set for each row so you end up lighting all at once, and then clock in new data while the last is showing..
5895s were $5 each, so looked heavily at multiplexing etc to fire the triacs way back when, just to reduce costs. Can be done but PITA and takes a lot of extra components and ends up having more failures, so didn't make much sense. A few sign drivers did do it commercially but again just didn't make much sense..
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Alan69
Joined: 01 Apr 2005
Posts: 76
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| 16 Feb 2008 5:27 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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http://www.superference.com/images/signs/Picture%2037.jpg
7 x 56 sign using 4094s/2003s for the chain to do the row. Was a piece of a larger sign, so I put my own transistors on the back to do the high side for each row. Send data for the row, turn on that row, then data for next row etc. Did this a long time ago, code is on a 16F84 from when the F84 just came out. Sign part is from a very old sign that was junked, one of the first that came out with the newer red super brights, so very early 90s.
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Mike, K8LH
Joined: 06 Jun 2005
Posts: 125
Helped: 15
Location: Michigan, USA
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| 16 Feb 2008 17:28 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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| blueroomelectronics wrote: |
| It's generally poor design to use a low I/O micro and a lot of expensive glue logic when a micro with more I/O would eliminate the glue logic. |
I'm sure you meant to qualify that statement with; "In my opinion...", correct?
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blueroomelectronics
Joined: 17 Sep 2006
Posts: 1140
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Location: Toronto, Canada
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| 16 Feb 2008 18:49 Replace TPIC6B595 with 74HC595 + ULN2803 |
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Ok, In my opinion. But that said I am using a 74HCT595 as an I/O expander in my next kit  I'm using a 40pin DIP and don't want to switch to TQFP.
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BeeBop
Joined: 19 Feb 2006
Posts: 164
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| 26 Feb 2008 22:51 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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| blueroomelectronics wrote: |
| Ok, In my opinion. But that said I am using a 74HCT595 as an I/O expander in my next kit I'm using a 40pin DIP and don't want to switch to TQFP. |
Ha ha, never say never, eh?
Looks like everybody is over here lately!
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Aurbo
Joined: 08 Jan 2008
Posts: 4
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| 23 Mar 2008 23:31 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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| pasicr wrote: |
Hi for all,
Am I thinking proprly?,
I can't find in my country TPIC6B595, this is ser in to par. out shift register for high current application,
can I substitute TPIC6B595 with 74HC595 + ULN2803,
best regards
p.s. I need this for that project
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pasicr,
Do you have the source code for this project?
Cheers
Aurbo
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pasicr
Joined: 13 Aug 2005
Posts: 249
Helped: 6
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| 23 Mar 2008 23:36 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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Hi Aurbo,
here is,
regards
p.s. Where are you from?
can you easy buy tpic6b595n,
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Aurbo
Joined: 08 Jan 2008
Posts: 4
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| 24 Mar 2008 16:08 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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| pasicr wrote: |
Hi Aurbo,
here is,
regards
p.s. Where are you from?
can you easy buy tpic6b595n, |
Thanks Pascir.
I'm in Canada, and yes I have access to the TPIC6B595N's
I actually have this project on the breadboard right now, but it does not seem to run. I've tested the 628 and 628A chips with another project and they both work fine. Writing this code and I get no results.
I'm hoping to find someone that has already created this project and could confirm the code actually works.
Regards
Aurbo
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muntron
Joined: 18 Feb 2008
Posts: 3
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| 28 Mar 2008 23:12 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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| blueroomelectronics wrote: |
It's generally poor design to use a low I/O micro and a lot of expensive glue logic when a micro with more I/O would eliminate the glue logic.
To run 4 seven segment displays takes only 11 I/O pins and 4 transistors so why not use a bigger micro?
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It is generally a bad idea to make general statements . There are times when it is better not to multiplex the display. If you are building a large display, it is a bad idea to multiplex as you now have to distribute many high voltage/high current signals over large distances. A serial interfaced latched display has advantages.
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cliffiv
Joined: 29 Mar 2008
Posts: 1
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| 29 Mar 2008 22:18 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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| I am Very new at this game and came acrossed the site while researching the TPIC6B595. I am making a larg seven seg display for my kids Lacrosse team and got the tpic's sampled for free the display has 5, 5mm LEd for each segment and i planned to drive it with the Picaxe8 to TPIC to 2803. Do i need to use the 2803's or can the TPIC handle 5 leds per a pin/channel?
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Mike, K8LH
Joined: 06 Jun 2005
Posts: 125
Helped: 15
Location: Michigan, USA
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| 29 Mar 2008 22:55 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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Dear cliffiv,
The TPIC6B595 is an 8 bit serial-to-parallel 50v 150ma 'sinking driver' IC so you don't really need the ULN2803 'sinking driver' ICs.
Mike
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Alan69
Joined: 01 Apr 2005
Posts: 76
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| 30 Mar 2008 4:43 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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But of course much cheaper to use a 74hc595 and uln2003 setup, the ones with built in drivers tend to be more expensive and harder to find. No real need to use 2803s, just stagger the 7 to 8 relationship, 2003s are generally half the price of 2803s or less..
Alan
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Mike, K8LH
Joined: 06 Jun 2005
Posts: 125
Helped: 15
Location: Michigan, USA
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| 30 Mar 2008 5:23 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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I think I would go for the TPIC6C595 in a 16 pin package. Available at approximately $1.11 or $1.17 (single quantity) at Mouser. That's actually very close to the price of a 74HC595 and ULN2803 combination at $1.24 (single quantity) also at Mouser...
But I also wonder if you couldn't drive this non-multiplexed display sub-system with just plain old 74HC595 ICs ($0.44 single quantity) and limiting segment current to around 10 ma? Oops! Never mind. Just realized that the 74HC595 outputs aren't open collector or open drain and so that would limit your choice of source voltages on the LED common anodes.
Mike
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Alan69
Joined: 01 Apr 2005
Posts: 76
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| 30 Mar 2008 14:40 Re: Replace TPIC6B595 with 74HC595 + ULN2803 |
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Heck that's a lot better than the ~$5 each for the uln5895s last I checked. But they do more like 500 ma I think. $1 is pretty reasonable for that TPIC.
Most ACT outputs do like 50 ma max, so if someone has a 595 or similar serial to parallel in ACT it could do that fairly legitimately. Probably over package dissipation with all outputs doing that, but would probably work fine. Likely still $1 anyway, so may as well get the TPIC for new, but might find an ACT version surplus somewhere..
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