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1  Using Arduino / General Electronics / MCP2515 CAN Controller Exposed Pad on: March 29, 2014, 09:47:46 am
Hi all,

I've just sent off for a board revision to be made, in which a swap between MCP2515 CAN controller packages from TSSOP to QFN was made, however - just quickly looking through the revised board again, I've just noticed no connected between the exposed pad of the QFN and ground.

Panicking, I looked at the datasheet

Unlike most devices, it does not specify a requirement to connect the exposed pad to ground, it just says see table 1-1, in which there is no mention of the thermal pad.

What would be everybodies opinion? No explicit declaration of said requirement = not required?
2  Using Arduino / General Electronics / Re: power leds driver on: March 07, 2014, 05:09:08 am
That depends, if you're just driving a couple and looking for a simple circuit - as long as you've got a constant voltage source that isn't going to spike and allow excess current through the LEDs, and size the resistor appropriately, then there's no problem.

Don't forget the thermal management aspect of power LEDs.
3  Using Arduino / General Electronics / Re: Clock out, CLKO, buffer requirements? on: March 06, 2014, 08:24:56 am
This is a project which dosen't involve the Arduino library or IDE at all indeed.

The programmer is no issue, I've got an ISP MKII & Dragon which I regularly use. Thanks for all the input.
4  Using Arduino / General Electronics / Re: Clock out, CLKO, buffer requirements? on: March 06, 2014, 04:58:42 am
It is somewhat frustrating that a fuse needs to be set to use it, I know... It would be nicer if there were a specific register access routine like that for using the watchdog that would enable you to use it.

It's none of the chips that come on Arduino boards I'm using, but AVR none the less. Thanks!
5  Using Arduino / General Electronics / Re: A/D converter 12 or 16 Bit on: March 06, 2014, 04:39:50 am

I'm looking for a A/D converter with 12 or 16 Bit and up to 10 V input range. DIP/DIL prevered.

Tried a product search on Digikey, Mouser, Farnell etc?

Why the jump from 12 to 16 bit? What about a 13, 14 or 15bit ADC? 12 to 16 is a huge jump in resolution.

Do you want a serial interface, or parallel etc? Your question is far too broad.

Also look at oversampling and decimation using the AVRs internal ADC if you don't need high conversation bandwidth.
6  Using Arduino / General Electronics / Clock out, CLKO, buffer requirements? on: March 06, 2014, 04:25:20 am
Having searched the datasheets for AVRs which support clock out, I cannot seem to find an equivalent circuit diagram or similar to answer my question.

I want to output my system clock to provide a clock souce for another device, to save on another crystal and caps - however, I'm just wondering if I need to buffer the clock signal prior to feeding it into another device - which would entirely defeat the point of trying to save on board space.

Logic would say no buffer needed, as the relevant section in the datasheet that says the system clock can be output is called 'Clock Output Buffer', so I'm assuming this is a buffer internal to the AVR.

Just thought I'd check before I commit a design?
7  Using Arduino / General Electronics / Re: better ADC for atmega328 on: February 26, 2014, 04:39:26 am
I presume he uses the filter on page 9 of the PDF he linked to.

8  Using Arduino / General Electronics / Re: better ADC for atmega328 on: February 25, 2014, 05:51:43 pm
I am using decimated oversampling to increase the 10-bit adc to 12-bit.

In order for that to work you have to include random noise with the analog signal.  If you are not doing that or do not know how to do that (I don't) then you most certainly should consider an ADC with higher resolution instead of trying to squeeze more resolution out of the AVR ADC.

The easiest way to do so is by adding the noise directly using a PWM signal through a filter into the AREF pin. I've used this successfully myself recently in a project, and you can obviously decide if and when you want the noise.

Page 9

To the OP, bear in mind any future requirement for increased sampling rates, as as I'm sure you know, you're eating into the ADCs bandwidth using the oversampling technique, so an external ADC will give you a little (well, a lot) of extra headroom.
9  Using Arduino / General Electronics / Re: On-by-default P channel MOSFET on: February 25, 2014, 04:00:57 am
So if the attached image was being used how would you change it to have the PFET be on at power up?
Take the end of R16 connected to ground in that diagram and connect it instead to +5V. I would make its value 10K instead of 1K.

I've got this schematic working no problem now - however, why is a BJT always used? Why not an n-channel FET, as then devices that come in a complementary N + P pair could be used?

Is it a technical, or typically cost driven choice?
10  Using Arduino / General Electronics / On-by-default P channel MOSFET on: February 24, 2014, 11:13:37 am
Hi all,

I feel like I'm having somewhat of a mental block this afternoon, I'm looking for a way to have a high side switched P-FET on by default.

Most drive circuits of course will have a pull down on the driving BJT to ensure that the circuit is off before any controlling MCU powers up, however - I need the FET to be ON by default, i.e. on before the MCU powers up.

Any ideas?
11  Using Arduino / General Electronics / Re: Save to EEPROM when poweroff on: February 23, 2014, 05:00:50 pm
Absolutely, have a capacitor in the supply large enough to give you enough time to save the data, and monitor the supply voltage using the ADC - when the supply is cut off,  the ADC detects this and you can enter the required function.

There's nothing to say you couldn't use a digital input either, and use external interrupts if you don't wish to poll an ADC reading or even poll a digital input. Although the ADC would be the best way to go about it, IMO - as you then have a continuous monitoring capability.

Most good designs should have the capacity to monitor it's voltage rails and have enough energy reserve to ride out brown-outs etc.
12  Using Arduino / General Electronics / Re: No connection to/with FT230X on: February 23, 2014, 04:53:35 pm
You got me, forum typo - I don't have the three nets, just GND & USB_GND. The latter is merely just a name for the net for which the USB ground pad connects to GND.

The confusion I presume came from the fact there is no actual USB connector on the board, but rather wires - and in an attempt to name each pad in EAGLE, it seemed the most logical way - but clearly not.
13  Using Arduino / General Electronics / Re: No connection to/with FT230X on: February 22, 2014, 01:44:16 pm
Sort of, yes and no.

One schematic page had all the through hole wire terminations for the board labelled up to their relevant nets, two of which were GND & USB GND, and also on that page was a net named USB_GND, which I had grounded using the USB pin, but there was indeed no connection to the actual ground net.

The only explanation I can think was that when the dialog box asking if I wanted to merge the nets, I must have by mistake hit 'no'.
14  Using Arduino / General Electronics / Re: No connection to/with FT230X on: February 20, 2014, 11:54:14 am
Problem solved... well, found.

I had named the USB ground net on one page, and linked it on another when laying out the PCB, which for some reason did not join the nets nor flag and error in EAGLE ERC, whether or not this is a bug I'm sure not - i'll need to investigate furthur on this.

It's fixable by bridging with a wire, but not good enough for me...
15  Using Arduino / General Electronics / No connection to/with FT230X on: February 20, 2014, 07:08:50 am
Hi all, I'm using an FT230X in a design of mine (the selection of which was discussed in another thread).

However, I've got my boards back and assembled a few - but cannot communicate with the MCU at all, in fact - the FT230X does not even appear in the device manager as a COM port.

I've downloaded the latest driver installer package, installed those - but when I power and connect the device over USB (device has it's own power supply, but can be powered by USB) - I get no connection in the device manager at all. Here's the schematic, the board is 3.3V so 3V3OUT is tied to VCC, as 3V3OUT becomes an input at 3.3V.

Here's a capture from the schematic, all as suggested by the datasheet. Any ideas?

Many thanks in advance.

EDIT - I've got the Rev D silicon by the way, as there was a bug in Rev B where VCP was disabled by default.
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