SN3218A 18ch PWM Board - schematic and board layout


Does anyone have the schematic to PCB layout connection pin diagram in a PDF or bitmap format?

And, what value resistor is the standard current resistor fitted?

Many thanks.

The default resistor is 332, A.K.A. 3.3kOhm, the recommended minimum.

We don’t have a published schematic, but the board doesn’t diverge from the reference implementation and is self documenting- Ground, Output Enable, I2C Clock, I2C Data and VCC are labelled along the top, and PWM channels 1 through 18 on the bottom.

That’s great thanks. I’ve wired it up accordingly.
The spec sheet says slave address 10101000, which is … 0xA8.
Examples in Python state address 0x54.
Which is it, do you think? (To be fair neither seem to work…)

I’m probably going to have to get a 'scope on it :(

I’m using a FEZ Cerberus and the Gadgeteer I2C library…

if you mean the I2C address, it is definitely 0x54… can’t remember if it is written on the silkscreen but that’s the address on the bus it should respond to…

Yep, 0xA8 failed with an I2C write error and 0x54 worked. At least as far as the software goes… No LEDs lighting up yet… :(

Well, I’m stumped. I can see data being written to the device on the 'scope, but nothing coming out of it LED wise. LEDs correct way around. Pull ups in place, OE high. I dunno. :(

Should I try on a Raspberry Pi? Will that standard software at least prove the module? Whats the most straightforward library to use?

are you sure you are using the correct register addresses?

The best approach would be to check the python library and see if the values used there are the same as the ones you are using:

Just to be sure, your LEDs are connected to a power supply and sinking into the PWM board?

Thanks everyone who responded. This has now been resolved - there was an out-by-one bug in the buffer write code in my (plagarised badly) I2C library.

Here’s a pic of the bodhran in all its multi-hued glory :)

And a closeup of the Pimoroni card in-situ

To any future readers, the address in 7bit is 0b1010100 not the 8bit 0b10101000 as stipulated by the datasheet. That’s mighty confusing!