Replace relays with solid state circuit

[ericgibbs]

Yes I could use 2 separate anode lines from the USB board but I would have to add another board for a total of 5 (max) and reprogram. It seems like a waste since the displays are always on, either green or red.
In that case we could add a transistor invertor for the colour select, leaving pins 8/11 on the ULN free for for the dp.

If I used a SPDT solid state relay for anodes like I mentioned that use 1.2v to control, how could I convert the 5v line from the USB board to 1.2v?

hi,
Can you post the part number for the SSR so that I can check it.?

 

[hiker]

The SSN is a Clare LCC110, Digi-Key (digikey.com) part CLA106-ND.

After taking a walk and thinking some more, I like your idea about separate lines for the red and green anodes. This makes sense in the long run, keeps things simple and now that I have cables of 10 conductors to each display is doable. This would require me to add another USB board which would control all 16 anodes (1 each red and green times 8).

I would greatly appreciate it if you could provide 2 more simple diagrams, each using the ULN2803A, one to control 8 cathodes and another to control 8 anodes (separate +5v supply) and using the same +5v control lines from USB boards. The reason for ULN2803A to control the anodes is that I do not think the USB +5v control lines provide enough power to light all the LED segments.

Thanks.

 

[ericgibbs]

The SSN is a Clare LCC110, Digi-Key (digikey.com) part CLA106-ND.

After taking a walk and thinking some more, I like your idea about separate lines for the red and green anodes. This makes sense in the long run, keeps things simple and now that I have cables of 10 conductors to each display is doable. This would require me to add another USB board which would control all 16 anodes (1 each red and green times 8).

I would greatly appreciate it if you could provide 2 more simple diagrams, each using the ULN2803A, one to control 8 cathodes and another to control 8 anodes (separate +5v supply) and using the same +5v control lines from USB boards. The reason for ULN2803A to control the anodes is that I do not think the USB +5v control lines provide enough power to light all the LED segments.

Thanks.

hi,
Will do, give me till Monday, its 19:00 in the UK.

 

[hiker]

hi,
Will do, give me till Monday, its 19:00 in the UK.

Very good, thanks.

 

[ericgibbs]

Very good, thanks.

hi hiker,

Look thru this drawing.

 

[hiker]

Thanks.

I cannot rely on the USB +5v supplying the current necessary to light all the LEDs in the segment displays. The anode circuit is much more complicated than I supposed.

I thought that I could connect +5-12v to pin 10 of the ULN2803A and the anodes to pins 18, 17 and the USB +5v control to pins 1, 2.

If you look at the schematic in my first post, the relay is controlled by a BC547C and a 1N4007 (the LED and resistor are optional). It seems to me the relay coil could be replaced with the LED anodes, could it not?

 

[ericgibbs]

hi,
The design covers all the points raised in your posts of yesterday.
Decimal point, computer buffering of the anode select, ability to individually select anodes, long cable runs, operation from +5 volts.

The anode select is the simplest I can think of one transistor and two resistors.

Perhaps other members reading this could come up with a better design.

 

[hiker]

OK, thanks.

What is pin 10 of the UNL2803A used for? You used it in the schematic of a previous post here.

Also keep in mind the the power to displays can be adjusted to a range 5v to 12v if it simplifies the design.

 

[hiker]

hi hiker,

Look thru this drawing.

https://www.electro-tech-online.com/attachments/hiker4a-gif.22518/

Hi Eric,
The cathode switching circuits using the ULN2803A works great. However, I have the components connected on breadboard for this anode switching diagram and it is not working as expected. Please help.

I am just testing one anode circuit, using pins 1 and 18 of ULN2803A. When I do not apply +5v to pin 1 of the ULN2803A the LED segment is on, and conversely, when I do apply +5v to pin 1 the LED segment goes off. So my results are the opposite of what I expected.

Also what are the capacitors for? Currently I am not using the capacitors.

 

[ericgibbs]

https://www.electro-tech-online.com/attachments/hiker4a-gif.22518/

Hi Eric,
The cathode switching circuits using the ULN2803A works great. However, I have the components connected on breadboard for this anode switching diagram and it is not working as expected. Please help.

I am just testing one anode circuit, using pins 1 and 18 of ULN2803A. When I do not apply +5v to pin 1 of the ULN2803A the LED segment is on, and conversely, when I do apply +5v to pin 1 the LED segment goes off. So my results are the opposite of what I expected.

Also what are the capacitors for? Currently I am not using the capacitors.

hi,
The ULN2803 is an open collector [darlington invertor].
When +5V is applied to pin 1 then pin 18 should go low [0.7v], this grounds the base resistor of the PNP transistor and switches it ON, putting +5V on the collector of the PNP. This +5V is the Anode supply to the far LED's.

Check that you havn't reversed the ZTX pins..

 

[hiker]

hi,
The ULN2803 is an open collector [darlington invertor].
When +5V is applied to pin 1 then pin 18 should go low [0.7v], this grounds the base resistor of the PNP transistor and switches it ON, putting +5V on the collector of the PNP. This +5V is the Anode supply to the far LED's.

Check that you havn't reversed the ZTX pins..

I've checked and rechecked and even reversed the connections to test. According to the datasheet for the ZTX450 it is a NPN transistor not a PNP. Is that the problem, and if so, what PNP transistor should I use?

 

[ericgibbs]

I've checked and rechecked and even reversed the connections to test. According to the datasheet for the ZTX450 it is a NPN transistor not a PNP. Is that the problem, and if so, what PNP transistor should I use?

hi,
I can see whats happened, it was when we were trying to find alternative transistors, I have misread the ZTX450.

If you recall the original type was ZTX751 which you couldnt source.

You require a PNP of the ZTX series that can run with a 200mA collector current.
If you can say which types you can get, I will suggest one from the list.

 

[hiker]

hi,
I can see whats happened, it was when we were trying to find alternative transistors, I have misread the ZTX450.

If you recall the original type was ZTX751 which you couldnt source.

You require a PNP of the ZTX series that can run with a 200mA collector current.
If you can say which types you can get, I will suggest one from the list.

Ahh... thank you.
The ZTX750 is the one I had trouble sourcing, previous post here. I can get the ZTX751, my source is here. Should I get the ZTX751 and use same circuit, just substituting the ZTX751 in place of the ZTX450?

Also do I need the capacitors, and if so, why?

 

[ericgibbs]

Ahh... thank you.
The ZTX750 is the one I had trouble sourcing, previous post here. I can get the ZTX751, my source is here. Should I get the ZTX751 and use same circuit, just substituting the ZTX751 in place of the ZTX450?

Also do I need the capacitors, and if so, why?

hi,

The ZTX750 and 751 are the ones I use. Pity you are not in the UK, I could give you some ZTX751's.

You do need the caps for noise decoupling, BUT you only fit one of each to the incoming +5V line, near to the ZTX's .
Not two caps for every ZTX.

Do you follow OK.?

 

[hiker]

Yes, I think I follow.
Here are the specs for the caps
electrolytic 220MFD/35V RADIAL CAP
ceramic 0.1 UF 50 VDC DISC CAP

 

[ericgibbs]

Yes, I think I follow.
Here are the specs for the caps
electrolytic 220MFD/35V RADIAL CAP
ceramic 0.1 UF 50 VDC DISC CAP

They will be fine, just one of each required.

 

[hiker]

OK, one more question please...

If I need to increase the voltage to drive the LED segments to make brighter, say to 6v -12v, will that change the resistor or other values?

 

[ericgibbs]

OK, one more question please...

If I need to increase the voltage to drive the LED segments to make brighter, say to 6v -12v, will that change the resistor or other values?

If you want to make them brighter and you increase the voltage and increase the resistors you will not get any improvement in brightness.

Just increase the drive voltage slowly from 5V until you get the required brightness.
The ULN will have no problems and the ZTX is rated to about 1Amp, so its just your power supply and LED's, dont exceed the rating of the LED's.

 

[hiker]

Hi Eric,
One more twist to this setup that I would like to pass by you...

There are two sets of 8 identical LED displays, each in separate rooms, that I was planning to connect in parallel. Since it's not necessary or desirable to have both sets on at the same time, I want to explore the possibility of switching one set on and the other off.

So I thought I could use both of your circuits together, the one here (Hiker 3) to switch the 5v supply between the sets of displays and the one here (Hiker 4a) to switch the anodes and cathodes of the individual displays. The Hiker 3a circuit could be controlled by a separate computer supplied 12vdc line. Hope you follow this.

I could use 2 4pdt relays in parallel to accomplished the 2 set switching but I'd like to avoid relays if possible. What do you think? Is using your two circuits together the best way? Keep in mind that about all I have remaining to control the switching from the computer program is one 12v control line.

 

[ericgibbs]

Hi Eric,
One more twist to this setup that I would like to pass by you...

I could use 2 4pdt relays in parallel to accomplished the 2 set switching but I'd like to avoid relays if possible. What do you think? Is using your two circuits together the best way? Keep in mind that about all I have remaining to control the switching from the computer program is one 12v control line.

Hi,
I have done a draft circuit to control each 1 of the 8 Green/Red anode selects.
If the control line is High its Green, if Low its Red.

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.?

If Yes, I'll finish the drawing.

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