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I am trying to send PWM, clock, latch and blank signals from Arduino through a series (16) of TLC5940 Breakout boards and on to a grid of 512 individual controlled LEDs six feet away (RJ45). I am using op-amps to help get the serial signals pushed through the large number of boards. Power and Ground are in parallel.

Of course, I am having problems. The set-up, as pictured, works well until the 9th or 10th board, then things get wonky. They are getting power but not individual control -just flickering.

I am trying to troubleshoot. The whole thing is powered by 12 V, 30 A switching power, buck converters for three different voltages (10 V for Arduino, 4.7 V for op-amps, 6V for boards and LEDs).

I am wondering if I should tie all grounds to a single common line back to the power source (V-) or do the individual voltages (10 V, 4.7 V, 6 V) need their own ground line back to power source? Example: the five op-amps - 4.7V+ and 12 V- single line common ground? - or should they have their own ground line all wired back to the 4.7 V converter and its 4.7 V-?

Power Diagram Full Diagram

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  • \$\begingroup\$ Did you check the voltage over the last boards? Isn't it just voltage drop due to long wires? (leave them connected to same ground as shown on picture) \$\endgroup\$ – Remco Vink Aug 30 '18 at 6:33
  • \$\begingroup\$ When I test the LAST (16th)board in the series, there seems to be near the same 6 V as the first (except I keep blowing out the first chip in the series:-) I was hoping that putting the Power and Ground in parallel would help that. They all power on after the ninth board, but with no individual control, just flicker. Unfortunately I can't or don't know how to test if the op-amps are working the signals past the first couple of them. \$\endgroup\$ – adlib33e Aug 30 '18 at 6:45
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Your DC-DC Modules have almost certainly an internal common Ground (Go ahead an measure resistivity). So you have them connected anyways. If you have problems the Power "Bus", as your diagram suggests, you should deploy a star configuration for your power, esp. ground.

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There's nothing inherently wrong with using power line buses. Star wiring might not solve the problem.

Ideally, you'd use an oscilloscope to see how stable the power lines are. But I'll assume you don't have one.

Consider centre-feeding the power lines, rather than feeding the power in at one end. That reduces the cable runs.

Consider using fatter wires. The volt drop in a thin wire could be too high. Digital devices often require sudden spikes of current, so the power lines could be dipping even if the average voltage measured by a voltmeter looks good.

Consider adding capacitors - electrolytic and/or ceramic - between the power lines and ground near each board (you already seem to have a few ceramic ones on some boards only). This could end up a bit trial-and-error. Too little capacitance won't achieve what you want, too much will overload the power supplies on power-up causing them to shut down.

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Just a word of warning - having multiple parallel ground lines designed for different currents is a recipe for disaster. If high-current power ground (e.g. LED) is accidentally disconnected all that current will go through (usually) thin wires for control supply. I've seen spectacular meltdowns of control boards connected by CAT5 for data and logic power and separate 10 AWG power lines.

From the picture in your question it seems you are using ubiquitous non-isolated Chinese DC-DC, which (again, usually) have common ground passing through. In this case it would be much safer to tie all supplies with just one ground wire to common bus.

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