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46  Using Arduino / General Electronics / Re: Using Microchip MCP2200 instead of FTDI FT232 on: October 18, 2013, 09:35:54 am
I can see why you would want to be able to control the GP pins from the USB side, for things like MCU hard resets - but to make them uncontrollable from the UART side seems madness...
47  Using Arduino / General Electronics / Re: Really noob question on: October 18, 2013, 08:22:39 am
When you look inside the DC jack (big black block that a DC power adaptor plugs in to),  you'll see a metal pin in the middle (that's the inner contact) and a sprung 'lug', that's the outer contact.
48  Using Arduino / General Electronics / Re: Using Microchip MCP2200 instead of FTDI FT232 on: October 18, 2013, 07:31:07 am
It seems the "+ 5V Single Supply Operation." line on the first page of the datasheet was copy and pasted from another FT device datasheet - as clearly it operates ona  3v3 single supply too...

Regarding the CBUS GPI/O pins - I've got a question, I can't seem to pull the answer out of the datasheet however. Can one manipulate the I/O pins using commands sent from the MCUs UART to the FT230X? Or can they only be manipulated by USB commands sent from a host computer to the FT230X?

The reason I ask, is i'm using an attiny device, and in an ideal world would have another 2 GPI/O pins that can be used to force sleep / shutdown in another device, instead of relying on timeouts - so it's not an absolute requirement, but it would be nice to be able to use the GPI/O pins on the FT230X to do this...
49  Using Arduino / General Electronics / Re: Using Microchip MCP2200 instead of FTDI FT232 on: October 17, 2013, 04:29:20 pm
Thanks, the rest of my board is 3.3V - so no problem there.

I'm glad to be 'back in the FTDI' camp as I know their drivers do work very well...

I'll have a read re the DTR line when I get a moment, see what my interpretation of it is - not that I need it...
50  Using Arduino / General Electronics / Re: Using Microchip MCP2200 instead of FTDI FT232 on: October 17, 2013, 01:39:18 pm
I don't believe the chip has a DTR pin, correct me i'm wrong but DTR is only part of the RS232 protocol, and not part of RS458 or any other protocol, and as a result is probably only supported by the bigger 'flagship' chips, such as the FT232R.

The FT230X is advertised as being an interface to a basic UART I suppose...
51  Using Arduino / General Electronics / Re: Using Microchip MCP2200 instead of FTDI FT232 on: October 17, 2013, 11:49:07 am
Lot of USB/Serial chips need an external also, while the FT232 does not.
MCP2200 seems to be one of those. Have you factored in additional cost (material, assembly) for 12MHz crysta/caps or a 12 MHz resonator?

I have yes - and the MCP2200 still works out cheaper with the crystal, caps and extra assembly than the FT232RL.

However, I had indeed missed the FT230 - which works out cheaper than both options indeed! Crossroads, why are you always so helpful?  smiley-cool
52  Using Arduino / General Electronics / Re: Using Microchip MCP2200 instead of FTDI FT232 on: October 17, 2013, 05:35:56 am
Farnell is the UK division of Element 14 over here, and their price are still much higher for the 232 than the MCP2200. My local assembly house has good buying power, but there's no getting away from the fact the 232 is just a much more expensive chip.
53  Using Arduino / General Electronics / Using Microchip MCP2200 instead of FTDI FT232 on: October 17, 2013, 04:27:24 am
Hi all,

I'm working on a little device at the moment, and need USB connectivity to the MCUs UART, so clearly need a converter chip like the FTDI FT232. However, the cost of the FT232 is astronomical  compared to a device like Microchips MCP2200, which is some 70% cheaper, which equates to a £132 saving before VAT in the qty i'm building them in.

Datasheet to the MCP2200 - http://www.mouser.com/ds/2/268/22228A-81933.pdf

I've never actually used one of these converter chips in a design before, and they all seem to talk about configuration tools in the datasheets.

To use these, is it really as simple as connect up the USB lines to the chips input, and the output to the UART (correct power, decoupling etc all of course) and talk away using a Virtual Com Port driver - which I presume would allow one to use the Arduino terminal to talk to the MCU. I presume the 'configuration' is a one time setup of the converter chip?
54  Using Arduino / General Electronics / Multipurpose input pin on: October 15, 2013, 10:08:39 am
Hi all,

I've been scratching my head over this for about an hour now - and seemingly can't get my head around it.

I've got a requirement, which I thought was quite simple. I'm using a 3v3 MCU (i.e. Due board), and have the internal pull ups enabled - then simply switch the pin to ground to signal a low. Elementary, done.

Now, a) I want the pin protected against ESD, so have a unidirectional TVS ESD diode connected to ground (http://www.mouser.com/ds/2/240/Littelfuse_TVS_Diode_Array_SPA_SP1003-221268.pdf). Good.

b) I also want the pin to be protected against against continuous overvoltage, i.e. somebody incidently connects the pin to 5V, 10V etc etc, so - adding some series R after the TVS, then a Zener just over 3.3v (MCU tolerance to 3.3 + 0.7V). So, if the pin is connected to 5V - the current is limited and the Zener clamps the pin to say 3.5V. Fine.

Here's the schematic - right hand diode is the TVS diode, left hand just a 'normal' Zener.  Note the input voltage to the ADC, 2.2V - seems there's lots of leakage through the diodes. I should really run this in SPICE later on, as opposed to cheap iPad app. [/URL]

Now - here's the challenge, I also want to be able to connect an analog voltage to this pin sometimes, such as a potentiometer, instead of a switch to ground, however - the pot is often likely to be supplied by 5V or 10V. Which isn't a problem in itself as the pin voltage is now clamped, but is is a huge problem in that it makes only a very small portion of the pot travel usable.

So, I tried running a quick sim with the pot feeding into a voltage divider (oh dear, divider into a divider!!!) as shown in the sim screenshot below - however, I'm getting all sorts of problems with the readings being thrown off by things like the pot value, reverse leakage through the diodes, leakage through the bottom of the divider etc, and so simply can't hope for any amount of accuracy at all.

The divider is sized so that at 10V, the output is 3.3V, but as I say - it's not that simple with all the leakages etc.

[/URL]

The 6.6meg resistor is the ADC input based upon the +-0.5uA leakage current into the ADC (which at 3.3V should give 6.6meg, R = V/I).

So, what am I to do - I need the pin protected against ESD, continuous overvoltage and able to read a potentiometer full swing from 0 - 5, 10 or 12V etc.

Many, many thanks in advance with this...
55  Using Arduino / General Electronics / Emulating diode behavior with transistors on: October 15, 2013, 05:06:59 am
Hi all,

I've come across a little problem here... I need to have a diode on the output of a high side switch, to prevent high voltage generated by a freewheeling motor from flowing back through the high side switch.

However, I don't want to use a diode as my load current may be well in excess of 5A, and even with a Schottky diode - the heat dissipation is unacceptable.

I'm looking for a low dissipation solution, so it looks like it will be some sort of active FET solution - but i'm stumped as to what sort of architecture. Using P FETs seem to present some issues, such as when the gate is pulled to 0V, the gate-source voltage could easily be exceeded and the gate destroyed depending on the voltage present at the source...

EDIT - I should clarify, the motor is a dual winding motor - hence when one of windings is powered, the other generates a high voltage, and one simply cannot shunt the high voltage to ground otherwise the motor is dynamically braked and stops spinning.

So another way I could word the question is - is I need to make it appear as so I have disconnected the slower winding completely from the drivers, when in reality I haven't.
56  Using Arduino / General Electronics / Re: Ultra high reliability capacitors on: October 08, 2013, 07:37:41 am
Quote
May we see the schematic?

Right now, no - but not being i'm being a pain smiley, but because this is just a general 'what-if' discussion at the moment, and in fact you've just taken the words out of my mouth.

Quote
If you are finding it necessary to place many large capacitors around your circuit, perhaps a design review is in order? Proper layout of power and ground lines helps, too.

I haven't yet found it necessary at all, as I'm yet to design and have the first PCB fabricated for this project so I have no idea if any issues are currently present. I'm rather thinking in advance, that if some filtering was in order - what are the more reliable options compared to the usual aluminium electrolytics.
57  Using Arduino / General Electronics / Re: Ultra high reliability capacitors on: October 08, 2013, 06:46:52 am
Quote
Sorry, bypass caps bypass rf or noise gliches in supply rails caused by digital switching or external emf, they are strategically placed physically around a pcb. They are usually of the order of  10uF down to 0.01uF depending on what you want to bypass.

I would refer to those as decoupling caps, as does most of the documentation I've seen.

I know bypass caps perhaps isn't the ideal description, but a number of sources still refer to high value capacitance in power applications as bypass, do they not?

But yes, you're right - the requirement here is filtering out noise created by PWM drive of various loads, in addition to bulk input capacitance to DC-DC converters etc.
58  Using Arduino / General Electronics / Re: Ultra high reliability capacitors on: October 08, 2013, 06:28:57 am
Enclosure and PCB wise, I have a size to which I simply cannot exceed - for a number of reasons. I will be looking at polyester film caps however, but PCB space is getting very tight indeed.

What do you mean when you say use ceramics though? Ceramics are used extensively throughout my design for decoupling, bootstraps etc. But I thought using large value ceramics was a BIG nono due to the high tendency for cracks to form?
59  Using Arduino / General Electronics / Re: Ultra high reliability capacitors on: October 08, 2013, 05:49:00 am
So, as I said I would - I've just been rereading this thread...

Whilst I see from many a source now that polymer tantalum are highly reliable caps - the main bypass caps used for power applications tend to be of the order of 1000s of uF. My input voltage can be expected to be as high as 30V, but no more.

From the searching I've done, it seems no polymer tantalum exists this large to suit such a requirement.

So, do I simply omit my bypass caps - and ensure that PCB trace parasitic properties etc are minimized as much as possible?

Also, I've got some high side P FETs driving loads with PWM, I had also planned on having each of these FETs with their own ~470uF caps (again up to 30V) to significantly reduce any noise that the switching would cause, clearly - one cannot do this with solid tants.

So, what is one expected to do?
60  Using Arduino / General Electronics / Re: Ultra high reliability capacitors on: October 04, 2013, 07:23:01 am
Aha, James - you must be the notorious capacitor expert on these forums whom I've heard so much about.

Thank you so much for your comprehensive and detailed reply, I shall be re-reading this a few times today.

I do intend to pot my design, and knowing now that aluminium electrolytics release hydrogen during use - will certainly not be using them, and will be switching to tant polymer caps.

I have also just been reading your blog post re the GSM shield failures - very interesting to see the effects of derating version polymer and non-polymer tants!

Thanks again.
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