as many inputs/outputs as i can get.

Design Concepts
1

hi, i need to have more then the max. 128 digital outputs. i assume i would need more than one core, but to do that, would i have to write a separate application for the second core?

also, if i didn’t need all the DINs, is it possible to ‘offload’ some of that band width to give me more outputs?

thanks

2

ok, just realised how much of a muppet i have been!

i need more than 128 LED outputs, and, as they are arranged in a grid, i can do a matrix, correct? 16x16 is just 32 connections.

sorry for waste of eye minutes.

3

having a bit of trouble understanding this:

http://www.ucapps.de/mbhp/mbhp_scan_matrix1.pdf

do the DINs work by sensing when the pins are shorted to earth? if so, how are they shorted? the DOUT pins they connect to are also at Vd, or have i missed something?

thanks

4

The last post you showed was for 64 Inputs in a matrix.

It works like this:

Set all outputs to HIGH.

Lower ONE of the outputs.

Read all eight inputs, the LOW inputs have switches closed to the ONE low output.

Raise the first output, lower the next one.

Read the next group of eight switches..

repeat until all eight banks of eight have been read,

then repeat everything from the beginning.

Now, if you need more OUTPUTS (for LED’s as you said)

It’s much the same, except you’ll use two sets of eight outputs,

and the diodes are replaced with LED’s, and the eight of those

outputs will need to be high-current (transistors will do) and you’ll

need eight current limiting resistors, and on and on..

I’d search a schematic for you, but I need to run an errand right now.

Good Luck,

Lyle

5

sorry, i should have really started on a new thread, i understand now you have explained it. thank you.

6

Now, if you need more OUTPUTS (for LED’s as you said)

It’s much the same, except you’ll use two sets of eight outputs,

and the diodes are replaced with LED’s, and the eight of those

outputs will need to be high-current (transistors will do) and you’ll

need eight current limiting resistors, and on and on..

ok, that bit i don’t understand! why is it that on the MIDIbox SID, there are no transistors? thanks.

7

I have not looked too deeply into the SID’s, but a quick glance shows that some of them have  a matrix of LEDs for display.

I can’t (quickly) find a schematic, so I’ll have to wing it here..

Assuming an 8X8 matrix, We’ll have each row connected to eight LED Anodes,we’ll call those 8 Group A,  and each column connected to eight LED Cathodes, group B. Let’s say you want the first Row with ON OFF ON OFF ON OFF ON OFF, a simple 4 on, 4 off pattern. So you set up group B with the on-off pattern you want, then enable them by turning on the driver for

the first Row. At this moment, only the first row has LEDs lit, and those are alternatinn ON and OFF as you arranged it.

Now look at your current draw. Four of the group B outputs are sinking enough current for one LED, the other four are not.

But the single ROW driver that is enabled must source enough current for all four of those LEDs. Under “worst case” it might be eight at a time. I would suggest that the PIC outputs will not source or sink enough current to drive eight LEDs on a single pin. Assuming 20 ma per LED, you may need to source 160 ma under the “brightest” conditions.

This is not an issue if you limit your displays to only a single LED in each ROW or Column, but when I design circuits, I like to leave my options open if I can.

I have not yet seen the schematic for these matrix displays, so I can’t say for sure what is doing the driving.

I may well be wrong, but I hope at least the explanation makes some sense.

LyleHaze

8

You don’t always need transistors, the 74HC595 outputs can sink (just) enough current to light a column of LEDs. If you prefer to have the LEDs brighter, use transistors, but also remember you’d need to invert the output… i.e. if you connect the base of a BC547 to the DOUT pin (with a 1k resistor), then the collector will sink current when the DOUT pin is high. So only one of the outputs should be high at a time, instead of one of the outputs being low.

The newer DIN DOUT module boards from SmashTV can have a darlington array chip fitted instead of the resistors (i.e. a chip of eight high-current transistors).

9

thanks lylehaze, that helps a lot. fyi, the sid DOUT schematic is here:

http://www.ucapps.de/midibox_sid_cs/mbsid_dout_default.pdf

thanks also to wilba, very helpful, but when you said:

The newer DIN module boards from SmashTV can have a darlington array chip fitted instead of the resistors (i.e. a chip of eight high-current transistors).

did you mean DOUT? i can’t see why a DIN would need high currents passing through it (nor, for that matter, stoned raisins. bah duhm tschh.).

thanks

10

Yeh he meant DOUT.

I would like to suggest that Mr modnaR be appointed unofficial forum jester

11

Yeah I meant DOUT.    ;D

12

I would like to suggest that Mr modnaR be appointed unofficial forum jester

i used to get laughed at at school too… ::slight_smile: ;D

Yeh he meant DOUT.

thanks, and…

Yeah I meant DOUT.   

…thanks.