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DIY Modular Test Equipment Project

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void_error:
Finally had some spare time to add the voltage regulator module for the analog sections to the draft branch of the related repo on GitHub.
As always, the link has been included first post.

void_error:
Wasted the whole weekend on PCB layout. Results in first post / on GitHub. There's room for improvement. I haven't included the footprint libraries although I will since there are some footprints I made myself. Not all parts have 3D models yet.

void_error:
There might be a problem with the +/-5V regulators on the waveform generator schematic, thought I'd redo some math on the thermal side of things and it looks like those LM317L/LM337L won't be too happy at a little under 50mA with a 15V input and I don't want to 'Rigol it' .

I have two options:
1. Use physically larger packages for the regulators
2. Move the analog supplies of everything using +/-5V apart from the AD603 to other rails.

I'm inclined towards number 2 since the DACs can take up to +/-15V and the LMH6642 can easily live off +/- 3.3V. Only the DAC for adjusting the offset will need to be run off +/-15V though.

As for option 1, I'm looking at D2PAK packages for LM317 / LM337 but those take up considerably more space compared to SO-8.

void_error:

--- Quote from: void_error on March 13, 2018, 07:37:31 pm ---I have two options:
1. Use physically larger packages for the regulators
2. Move the analog supplies of everything using +/-5V apart from the AD603 to other rails.

I'm inclined towards number 2 since the DACs can take up to +/-15V and the LMH6642 can easily live off +/- 3.3V. Only the DAC for adjusting the offset will need to be run off +/-15V though.

As for option 1, I'm looking at D2PAK packages for LM317 / LM337 but those take up considerably more space compared to SO-8.

--- End quote ---

Yet again I realize I didn't have my head screwed in properly and while both of the above would work the voltages need to be +/-5V so there's no need for adjustable regulators. 7805/7905 will do just fine. As far as the case goes, D2PAK is HUGE and SO-8 can't handle half a watt... at least with a temperature of 50C inside the case which isn't likely since there's going to be a fan in there.

Luckily the 7805/7905 also come in DPAK cases which are considerably smaller than the chopped up TO-220 which is the D2PAK, they're roughly the same size as an SO-8 and have significantly lower thermal resistance, under the form of 78M05 and 79M05. Junction to ambient thermal resistance doesn't exceed 100C/W so that's only a 50C rise for 0.5W (10V drop @ 50mA) which is well within acceptable limits and real world thermals will be significantly better since it's mounted on a PCB. Problem solved. I choose option 3.

void_error:

--- Quote from: void_error on February 23, 2018, 06:02:51 pm ---waveform generator 115x95mm.

--- End quote ---

Nope. That was a bad idea. Plus the case which was my initial choice would have ended up being mostly filled with air so I'm swapping it with this one and making the waveform gen PCB 175x70mm.

Just so this is more fun, it looks like differential signalling might be required since the traces are getting quite long, not to mention that adding a ribbon cable would make things a lot worse. That means adding some differential transceivers and have the UART over RS-485, use RS-485 transceivers for SPI like metioned here, same for the GPO and GPI, differential signalling for the clock (haven't looked into that but it should be able to handle 16MHz), should get away with single ended for the 400kHz regulator sync signal as long as it's buffered on every board I think, the 1-wire bus should be fine since it's really slow anyway.

The only thing I have no idea what to do with is I2C. Any suggestions?

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