Replace relays with solid state circuit

[hiker]

The computer program line you have 'spare' to control 'Group A' and 'Group B' banks of 8 Displays, can you select it +12V or 0V.?

ie: +12V = say Group A and 0V = Group B.
Is this what you mean.?

Yes, you have it right.

Group A is 8 remote displays and Group B is the other 8 remote displays.

Correct.

Thanks

 

[ericgibbs]

hi hiker,
Look over this pdf, if its not quite want you want, copy and paste and make a new drawing and post it.

Regarding switching Groups A and B on.off.
By using the +12V/0V from the computer you can only have A or B group ON

It would be far simpler and cheaper just to set the segment pattern as all OFF when you want to blank a Group. ie: no Group switching required.

This would enable you to select either Group 'A' or 'B' in any combination.
Also it would reduce the number of computer lines required.

 

[hiker]

Hi Eric,

It would be far simpler and cheaper just to set the segment pattern as all OFF when you want to blank a Group. ie: no Group switching required.

If I understand you correctly, this is not possible because there are not enough computer lines to switch all the segments of 16 displays. There are a total of 80 lines, switched by the computer to 0v/5v. So 8 segments x 8 displays = 64 for cathodes, plus 8 displays x 2 for anodes = 16, grand total of 80 for 8 displays max.

I'm having a hard time following the new diagram, Hiker#5. I think it assumes that I am using just one line to power the green and red anodes. However, we changed that since there are two separate lines for each red and green anode. Refer to Hiker#4a diagram which is what I am planning to use for anode switching.

Hiker#3 was your diagram for switching between red/green anodes before we decided to use separate lines and the result was Hiker#4a. I have tested a combination of the two to do the A/B group switching by using Hiker#4a as is and Hiker#3 to be fed from the anode lines at the right side of Hiker#4a diagram. Not sure if I can make a decent diagram to show, are you using a special program for schematics?

All I did for my test was to set up the components on breadboard for both Hiker#3 and Hiker#4a with 2 separate LED 7 seg displays. After both worked separately, I made the modification to feed each display as in Hiker#3, right side labeled Green and Red, now Display#1 (group A) and Display#2 (group B). Now the +5V in the center of the Hiker#3 diagram is tied to the anode output on the right side of Hiker#4a. With this setup I would need 16 of the Hiker#3 circuits, one for each of the Red/Green anodes, to do the A/B group switching. To control the A/B switching I am using a 12v line and one leg (pin 8) of a ULN2803A as in Hiker#3

I'm not sure if this is the best method, but it works. Also I tested with only one of each Hiker#3 and Hiker#4a circuits, and I'm not sure after all circuits are tied together, the best way to use the common 12v line to control all 16 of the Hiker#3 A/B circuits. Is a ULN2803A really needed since I think I only need one input leg and could tie the output leg to all 16 in parallel to the control input of Hiker#3? Could a single darlington transistor be substituted for for the ULN2803A in this case?

Any thoughts?

 

[ericgibbs]

hi,
Have read thru your text description, I would suggest that you do a drawing of the project, using any of the common drawing programs.

Also show where the proposed darlington will be in the circuit,

 

[hiker]

Attached 2 diagrams with comments.

 

[ericgibbs]

Attached 2 diagrams with comments.

Downloaded them, will work thru them.

 

[ericgibbs]

hi,
It would be doubtful if the computer driving source for the 12V/0 for the 16 inputs for the ULN2803 would upto the driving the load.
Also its going to be an inefficient way to do it.

I'll look at some other simpler/cheaper way to do it and post, Mon 6th.

 

[hiker]

OK, good. I think the 12v line can deliver 200-300 ma max. It's actually coming from an A/V switcher that is controlled by the computer. I can't find the exact specs so I'll call the factory on Mon.

How much current would be needed to drive 16 of those circuits? The 12v 4pdt relay coils I looked at each take 75 ma and I would need 4.

 

[ericgibbs]

OK, good. I think the 12v line can deliver 200-300 ma max. It's actually coming from an A/V switcher that is controlled by the computer. I can't find the exact specs so I'll call the factory on Mon.

How much current would be needed to drive 16 of those circuits? The 12v 4pdt relay coils I looked at each take 75 ma and I would need 4.

hi,
Regarding the current loading for the displays.

Assume 15mA to 20mA per segment, including the decimal point its: 8 * 0.015 = 120mA or 8 * 0.02 = 160mA.

Taking the lower figure of [15mA/seg], 120mA for 8 LED's in Group 'A' gives, 8 LED's *120mA = 960mA, say 1Amp

So when all segments of Group 'A' and 'B' are lit it gives a worst case current requirement for the LED's of 2Amps.

The transistor switching requires just a few tens of mA's, say 25mA.

Regarding the 4 relays, 4 * 0.075 = 300mA when all energised.

If you decide to power the LED's and relays from one 12V psu, I would suggest a 2.5A to 3A rated psu.

IMHO the ON/OFF switching selection for Group 'A' and 'B' would be best suited to a relay,
no voltage losses across a series transistor and it would cheaper/simpler.


Perhaps if you posted details of the full project, I could make some suggestions that may help.
It appears to me that the computer/circuit is over complex and inefficient for what you are trying to do with the displays.

At the moment I am just seeing a 'bit' of the project which makes it very difficult for me to hit the target.

 

[hiker]

Hi Eric,
I'm attaching a logic diagram of the project.

Thanks

Note: Omitted from the diagram is the 12v line from the computer to the A/B anode switch.

 

[ericgibbs]

hi hiker,
This is the circuit as explained in our PM's

Note: it uses those ZTX 450 to drive the bases of the TIP's

 

[hiker]

OK, thanks.

So I would need 16 of those circuits (one for each anode)?

And the "+V in" would be tied to the anode switching circuit output (Hiker#4a)?

Could I use ZTX649 in place of ZTX450? (I can get those locally and cheaper)

 

[ericgibbs]

OK, thanks.

So I would need 16 of those circuits (one for each anode)?

And the "+V in" would be tied to the anode switching circuit output (Hiker#4a)?

Could I use ZTX649 in place of ZTX450? (I can get those locally and cheaper)

hi,
Checked the ZTX649 npn looks OK.

In either Room A or B, will the enabled room LED's be all the same colour.?
It makes a difference to the final layout.

Look at this block1 diagram, mark it up to suit your idea.

 

[hiker]

In either Room A or B, will the enabled room LED's be all the same colour.?

I'm not sure if I understanding your question. The computer can switch any number of the displays (one, two or all) either red or green by switching the appropriate anode on or off. Normally, by the logic of the switching of the A/V switcher, all but one will be green. The purpose of the A/B room switch is to prevent all 16 displays from being lit since only one room is ever in use at a given time. There is one display on each of 8 TV monitors per room.

The diagram looks correct, except that the 12v line from the computer shows a block labeled "ULN" which I don't see in your last A/B schematic. Does that block represent your circuit? Commented diagram attached.

 

[ericgibbs]

I'm not sure if I understanding your question. The computer can switch any number of the displays (one, two or all) either red or green by switching the appropriate anode on or off. Normally, by the logic of the switching of the A/V switcher, all but one will be green. The purpose of the A/B room switch is to prevent all 16 displays from being lit since only one room is ever in use at a given time. There is one display on each of 8 TV monitors per room.

The diagram looks correct, except that the 12v line from the computer shows a block labeled "ULN" which I don't see in your last A/B schematic. Does that block represent your circuit? Commented diagram attached.

Thats answered my question, I'll revise the dwg based on your reply and repost it, also the circuit for the A/B switching.

Do you have any idea what the +12v/0v line can switch in terms of inputs.
There are limits to the number of inputs a single line can drive. It may be necessary to have a buffer between the anode switching transistors and the single 12V/0V line.

 

[blueroomelectronics]

From what I've read is the final product: two sets of 8 digit seven segment Red/Green displays? How large are the digits?

 

[hiker]

Do you have any idea what the +12v/0v line can switch in terms of inputs.

Do you mean how much current? Max is about 200ma supplied through a power source in the A/V switcher (not in diagram) controlled by computer.

Wow you're up late tonight.

 

[hiker]

From what I've read is the final product: two sets of 8 digit seven segment Red/Green displays? How large are the digits?

Only one digit each display, 8 diplays each room, 1" high.

 

[ericgibbs]

hi hiker,
This layout should be close to the final stage.

The Type 'A' circuits are the ULN2803 segement sinks, 8 ULN2803 plus resistors

The Type 'B' circuits are for anode colour selection, 16 total [ thats 8 for each room].
The inputs are connected directly to the USB/Comp output, no ULN.
The USB output pins, each one drives two anode select circuits.
Duplicating the anode select circuits makes the Room selection simpler.

The Type 'C' circuits are for Room selection, 1 total, the input for the Room select circuit is the +12V/0V comp line
or you could use one of the spare 8 outputs on USB/expander #5

Operation example.
Set Room Select to 0V, thats Room A.
Select the individual digit anode colour, say all RED, so USB output is high.
Select the individual digit pattern for all the LED's

Its seems an awful of circuitry to control 2*8 LED's... Good Luck.

 

[hiker]

Wow that's a lot simpler. Thanks.

Some questions...

Some of the transistors are not identified, namely Q1, Q2, Q4, Q6. Please identify as type.

Is it OK to use ¼W resistors? I've been using ½W.

Since the ZTX649 is in short supply at my local source, I'll probably use ZTX450 instead for NPN ZTX type, OK? And ZTX751 for PNP ZTX type. And TIP32C where you have specified TIP32, OK?