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Topic: Limits of stringing of 74HCN595's (Read 3 times) previous topic - next topic

carbine000


What do Pin0, Pin1, etc go to? The Arduino?
You are feeding shifting from  the bottom one into the top one?
I'd have to review the datasheet again to confirm the shift-out to shift-in connection, but I'd say you have the idea.


Well I just connected everything best I could. I'll be honest I don't fully understand what all the pins do on the 74ACT299. I have a good understanding of what is going on with the 74HC595's thanks to these tutorials:

http://www.arduino.cc/en/Tutorial/ShiftOut
http://www.codeproject.com/KB/system/ArduinoShiftRegisters.aspx

On the 74ACT299:
I don't understand why there are two function select inputs and why there are two enable inputs.
I don't understand a lot of the inputs to be honest. Which is the latch pin? Which is the data pin?

I still don't understand why this is better than using the 74HC595s but I think I have an idea of what is going on just not as much as with the 74HC595s.

I was thinking about the 74ACT299 and maybe 24mA per output could potentially be too low. I know it can vary but I don't think any 5mm LED will go over 30mA for any color. And, it's a bit hard to tell without physically having the LEDs since a lot of ebay sellers seem to be just copying/pasting the data for their LED's (or that is the way it looks to me). So I think something that can sink 30 mA per pin would be enough to ensure maximum brightness for all LEDs and all LEDs can be on simultaneously.


CrossRoads

The 74AC299 is better for its current sink/source capability. The 74HC595 was designed to interface with other logic chips, not for driving LEDs.

24mA will be plenty. Most LEDs have limits of continuous On current approaching 30mA.  Don't plan on running them that high.
If you get some 20mA, 5,000mcd LEDs from dipmicro.com for 5-6 cents, or from superbrightleds.com, they will  amazingly bright at 20mA.
I just just used some of the reds, 2 in series with 100ohm resistor, and 2 blues in parallel with single 200 ohm resistor, they are bright.
If you are buying 20mcd LEDs, those will not be too bright at all.

I have 20 74ac299s on the way from newark.
download this datasheet
http://www.national.com/ds/54/54F299.pdf#page=1
I think it makes it a lot clearer what the connections are.
The part can be parallel loaded (vs just shifting in from 1 pin), and the bits can be shifted left to right, or right to left. So more of a universal part, can be used as a shift-in or as a shift-out register.
I will do some reading and check back in tomorrow.  Have a pounding hedache tonight for some reason.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

carbine000

I'm sorry to hear about your headache. :(

What does right shift and left shift mean?

CrossRoads

You can shift from Q0 towards Q7, or from Q7 towards Q0.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

carbine000

#19
Mar 04, 2011, 08:31 am Last Edit: Mar 04, 2011, 08:38 am by carbine000 Reason: 1
Ok that was the datasheet for a 54F299 but you are saying to get the 74AC299S right?

So using it as a current sink we are actually using the I/O as inputs?

It says on the datasheet that the DC VCC or ground current per output pin is +/- 50 mA what does  that mean?



CrossRoads

You want to 74AC299PC to get the DIP parts, unless you are after surface mount.
Should have been this datasheet, I saw the 299 and copied it by mistake.
http://www.national.com/ds/54/54AC299.pdf

Same part, screened for MIL temp range.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

CrossRoads

Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

carbine000


You want to 74AC299PC to get the DIP parts, unless you are after surface mount.
Should have been this datasheet, I saw the 299 and copied it by mistake.
http://www.national.com/ds/54/54AC299.pdf

Same part, screened for MIL temp range.


What is the difference between DIP and surface mount?

CrossRoads

DIP is Dual Inline Package, the parts with 0.3" spacing & pins with 0.1" spacing that will plug into a solderless breadboard.
The ATMegae328 on the Duemilave is a DIP part. The FTDI is surface mount.

Surface  mount are much smaller packages.
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

carbine000

I am definitely going to need to solder these things down.

Ok so I am going to get 74AC299PC for my shift registers and that will act as a current sink because it has input/output capability unlike the 74HCN595 which is just output.

I am also going to get common anode LEDs instead of common cathodes.

So. Parts:

1. 74AC299PC
2. common anode RGB LEDs
3. Current limiting resistors for the LEDs (I'll figure out which kind I need after I get the LEDs)
4. Arduino Uno

Sound good?

CrossRoads

Yes.
Get some 0.1uF caps for decoupling the '299s as well, one across each devices Vcc/Gnd pins.
Going to have a lot of switching going on, will help keep power supply noise down.

Are you making a PCB, or wiring it all by hand, either wirewrapping or point to point soldering?
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

carbine000


Are you making a PCB, or wiring it all by hand, either wirewrapping or point to point soldering?


I was planning on just using breadboards from the electronics store and hand wiring everything.

I think making a PCB might be the best way to go. I want something cost effective and time effective as well. What do you think I should do?

I'm going to be connecting almost a 100 of them up. I was thinking a PCB with a group of 3 of them together would perfect.

CrossRoads

Are you comfortable with Eagle for schematics and layout?
If so, you can get a 10" x 10" board here for $95.
Layout your design so it is modular in eagle-light (only get 1 page schematic to fit what you can), have them duplicate it across the board area for you.
Or get someone with a full blown eagle package to help, maybe like liudr (search members to PM  him).
https://www.internationalcircuits.com/layer_grid.php?cat_id=13
Designing & building electrical circuits for over 25 years. Check out the ATMega1284P based Bobuino and other '328P & '1284P creations & offerings at  www.crossroadsfencing.com/BobuinoRev17.
Arduino for Teens available at Amazon.com.

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