PCB layout - JHarvey

[MotoFab]

If there are spare FETs included they should be attached to the port P pins for PWM use.

If one SPI port is allocated from port P, that leaves 4 remaining pins for PWM use.

- Jim

[jharvey]

I got to find out that in KICAD you can save to a local module library (/home/blah/ect) rather then the system library (/usr/share/kicad-or equiv) by using the export command rather then the new library command. This means we can include the modules in the source directory, and not need to copy files around.

Modules I'm working on inlcude a combined verision of R4 and SM0805 that I'm calling R4-SM0805, and I'll be doing the same for caps. I plan on most R's and C's to be thru hole as well as SMD. Then users can choose what they like to solder.

[Fred]

Awesome Jared, you're a hero :-)

Fred.

[davebmw]

Evening dudes!

I have been laying out the new CPU area of the PCB today. I have designed the 112 pin LQFP footprint and sorted it in a library.

Firstly the LDO regulator gets really hot does anyone have any objections to ether getting rid of it totally of the CPU card and or using a high efficiency switching regulator circuit?

i have got the basics started MCU, oscillator, supply rails, etc, I'm about to start on the comms i know we need RS232 may as well use both channels on the 232 interface chip. question is do we need RS 485? CAN if so how many?
Do we need BDM port?

I have noticed that there is an LED on PP7 a PWM port, why is this there can we get rid of and free up a PWM port?

What other requests do we require of the CPU area or a pin for pin replacement for the TA card?

I need to know before progressing further.

[jbelanger]

You will need a BDM port if only to program a bootloader into the new CPU.

The LDO regulator (I assume you're talking about the TechArt board) gets hot because it's only a 100mA part if I remember correctly. Fred had the same issue initially and changed it. It should be in one of his posts. I don't know why they don't spend the few cents more it would take to have one with a reasonable current rating.

Jean

[davebmw]

OK i have found this nice very capable LDO linear reg:

http://uk.rs-online.com/web/search/sear ... &R=5339404

LM1085IT-5.0, 5.0V, 3A, max 20V in, £2.15 from RS i'll get discount on that.

BDM port ok done.

Pardon my ignorance but what is JB1 used for it has 2 signals MODA and MODB, is this a requirement or can it be swept under the carpet??

[Fred]

Firstly the LDO regulator gets really hot does anyone have any objections to ether getting rid of it totally of the CPU card and or using a high efficiency switching regulator circuit?

Even the correct LDO will get really hot unless it is heatsinked appropriately. I think I'd rather have it radiating heat into a sink that potentially radiating switching noise into the CPU wouldn't you?

question is do we need RS 485? CAN if so how many?

One CAN and no to 485.

Do we need BDM port?

As Jean said :-)

I have noticed that there is an LED on PP7 a PWM port, why is this there can we get rid of and free up a PWM port?

Currently it's used as a "I'm alive" LED for when you first load your flash new code. I think for noobs this is a good thing to have and although it's across the port, the port is still free to be used for something else, the LED will just mimic the device. In summary, do as you please with it :-)

MODA and MODB are for selection chip operation modes. We can actually use those pins as IO too, here are my notes about them :

Using as input will result in random behaviour, output goes low during reset

I'm going to post a picture proving something you said was very right in a few minutes.

Fred.

[jbelanger]

OK i have found this nice very capable LDO linear reg:

http://uk.rs-online.com/web/search/sear ... &R=5339404

LM1085IT-5.0, 5.0V, 3A, max 20V in, £2.15 from RS i'll get discount on that.

That a nice part but be careful about the pinout because it's not the same as the more common LM2937/LM2940.

By the way, why does RS link to the Japanese datasheet?

Jean

[davebmw]

Even the correct LDO will get really hot unless it is heatsinked appropriately. Agreed! dissipation is dissipation the laws of thermodynamics are pretty clear on that.

I think I'd rather have it radiating heat into a sink that potentially radiating switching noise into the CPU wouldn't you?
switching reg circuits only do that when designed by a complete muppet! correct use of reactives on the OP will kill all HF Ripple, but a linear reg is much simpler if not a bit less efficient. i'll keep it simple

Fred.

OK Cool thanks guys if there are any other features you want in the CPU area let me know and i'll squeeze them in.
Do you have a preferred USB module so i can design in a header for it, if there is one that can act as a host for data storage that may be handy.

[Fred]

OK Cool thanks guys if there are any other features you want in the CPU area let me know and i'll squeeze them in.

Yeah, put a couple of pins for the bootloader and reset jumpers/switches/headers etc. I like a bootloader switch on the outside of the case and a momentary reset switch is invaluable while testing and messing around. The bootloader needs something but the other one is optional and maybe even a bad idea.

Fred.