I want to mount 60mm Matrix LEDs to the board. My thought is to mount female headers to the board and solder on the back. I want to be able to remove the LED matrixes without otherwise disturbing the board. But, I don't want the solder to provide all the mechanical strength. Is it a good idea to put some adhesive on the header? My thought is to put the header on the board and apply the adhesive on both sides of the header, not under it because it would get on the pins which I don't want. Does this make sense? What would be a good adhesive for this purpose? I would love to know a specific brand if you have a favorite that would be good for this application.
Thank you.
Side view of mounting (H = header, A = adhesive, B = the PCB, P = the exposed pin for soldering)
Use solder only. Is stronger than any any adhesive you can come up with.
When I build on boards like that, I use wirewrap socket strips and generally just solder the two end pins, and it if s a long strip I'll solded one pin in the middle too.
I don't do point to point soldering for digital stuff anymore, too messy if you need to make a change or correct a mistake.
CrossRoads:
Use solder only. Is stronger than any any adhesive you can come up with.
When I build on boards like that, I use wirewrap socket strips and generally just solder the two end pins, and it if s a long strip I'll solded one pin in the middle too.
I don't do point to point soldering for digital stuff anymore, too messy if you need to make a change or correct a mistake.
Ok, so you think wire-wrap it? That is a different kind of socket. Do you have a link to a good supplier of wirewrap socket strips that are like female headers? I don't even see those at Jameco or Digikey, though I see very expensive DIP sockets. I had given a thought to wire wrapping, and I understand in principle how to do it, but all I have ever seen are DIP sockets and not SIP ones that I need for these matrices.
Thanks. I just priced some of that company's wire wrap products vs Jameco and they do have good prices. I ran it through the shipping process and their shipping rates are terrible, about 3x what Jameco charges me for the same distance and weight (I priced 40 of those SIP sockets, not exactly a heavy load and less than a pound). They should ship USPS, that is a good deal and USPS gets it from CA to IL in 2 days. If I make an order, I will have to make it a pretty big one just to make it worthwhile because that is probably not a well I would like to drink at very often giving the shipping rates. I will reconsider how I am going to do this project and think about it.
I ordered a lot of parts from them, and the shipping was still not very good.
You know what to look for now, if you find a better source let me know about it
Actually, now that I think about it, I have another issue with wire wrapping other that sourcing components and their price.
I intend to mount 12 bicolor 60mm LED matrices, in a 4x3 configuration, but electronically it is going to be 1x12 with 8 PNP transistors driving the rows and 12 TLC5940s sinking the columns. So the problem is that while the columns sink about 20ma the rows have to drive up to (worst case) 2.88 amps, though I am planning on displaying mostly text so I don't see more than 10-20% of the LEDs being lit at any moment. Row selection will be done by a 3:8 decoder (74138) with a 1/8 duty cycle. Is that too much current to do wirewrap on?
Do you think a TIP42 is OK for providing current this application or might that transistor be too slow? The switching of the rows will be, hopefully, at 800Hz for a complete refresh at 100Hz. Thank you.
You're running from 5V?
How are you calculating 2.88 Amps?
That's be 144 LEDs on at once.
You are multiplexing, yes? I don't see how you'd have that many on at one time.
CrossRoads:
You're running from 5V?
How are you calculating 2.88 Amps?
That's be 144 LEDs on at once.
You are multiplexing, yes? I don't see how you'd have that many on at one time.
What I said was:
So the problem is that while the columns sink about 20ma the rows have to drive up to (worst case) 2.88 amps, though I am planning on displaying mostly text so I don't see more than 10-20% of the LEDs being lit at any moment.
The calculation only considers one row being driven. 12 displays * 16 columns each * 20ma = 3.84 amps. The figure I gave before was wrong and low. I am not sure how I did that because this is the calculation I used. If everything was lit it would be 3.84 amps continuously because it is driving one row at 3.84 amps at any given moment, though the row changes.
And I did say that I expect no more than 10%-20% of the columns to be lit. This is still .768 amps. The chart gives the maximum for 30 AWG as 0.86 ampere for "chassis wiring" or 0.142 ampere for "power transmission", but I have no idea what these terms mean. If my application is chassis wiring, I guess I am good if my 20% guess is accurate and the software does not malfunction.
I have found a definition for chassis wiring here:
and
and I am convinced this is a chassis wiring application. I think this would be a fun way to learn wire-wrap and we are under the limits so I am going to give that a try. Thanks!
You mention 12 TLC5490s, so you seem to intend 1 per chip.
Each TLC5490 will pull 1 row shall we say, then the next row, then the next row, until all 8 rows are done.
So worst case, you have 12 x 16 LEDs on at any one time.
12x16*.02 = 3.84 Amp.
Okay, you may want to split the row up into 4 pieces with a separate anode driver for each, or go to P-channel MOSFETs which will run much cooler.
Thanks, that is probably smarter and will keep the current down on the rows. I would think 3 pieces, though, make the row drivers separate for each of the 3 actual rows of matrices. That probably gets it where it needs to go and it appeals to me because of the symmetry. It requires another 16 transistors and 32 resistors, but at least those are inexpensive parts. Thank you for your insight on this.
