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Topic: Bus Pirate v4 hardware  (Read 72078 times) previous topic - next topic

Re: Bus Pirate v4 hardware

Reply #90
[quote author="fenugrec"]You have a good point about the USB current draw. I was just accounting for the quiescent current; I don't have the MIC datasheet handy but it probably is <5mA.[/quote]To phrase my point more concisely, the Enable input is not designed to get rid of the quiescent current, it's designed to stop the attached load from drawing any current.  It basically acts as a soft power switch.

The Bus Pirate has the feature of allowing other devices to be attached and potentially take their power from the Bus Pirate, and thus you can never guarantee how much current will flow.

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That's my point - I was evaluating the necessity of having a 5V regulator on a board powered by... 5V !
The only times it would regulate would be when the USB bus is supplying appreciably more than 5V. In most cases I've dealt with though, the ~5V supplied by the USB port is quite good enough to act as a generic, low(ish) power supply for microcontrollers, small projects, etc.
So my question would rather be : who would need the onboard 5V regulator, and in which context ?
I'm thinking it possibly isn't needed by a vast majority of users ?
The problem is that you really need to pay careful attention to the requirements of the chips you're working with.  The vast majority of 5 V chips are only specified to work with 5 V +/-5%, meaning 4.75 V to 5.25 V, but USB will not deliver this in all situations.  Why take the risk of spending money on a design when it might not work when you need to add an unpowered USB hub in order to expand your ports?

Thanks for bringing up this topic.  I had not reviewed the Bus Pirate schematic in detail before now, or I would have pointed out the problem with the 5 V regulator.  Basically, the Bus Pirate needs to be redesigned with a 5 V boost regulator instead of a standard regulator.  Otherwise, as you point out, there is not much use in having a feature which could so easily fail to work properly, given the USB environment.

Re: Bus Pirate v4 hardware

Reply #91
[quote author="rsdio"]To phrase my point more concisely, the Enable input is not designed to get rid of the quiescent current, it's designed to stop the attached load from drawing any current.  It basically acts as a soft power switch.

The Bus Pirate has the feature of allowing other devices to be attached and potentially take their power from the Bus Pirate, and thus you can never guarantee how much current will flow.

[...]
The problem is that you really need to pay careful attention to the requirements of the chips you're working with.  The vast majority of 5 V chips are only specified to work with 5 V +/-5%, meaning 4.75 V to 5.25 V, but USB will not deliver this in all situations.  Why take the risk of spending money on a design when it might not work when you need to add an unpowered USB hub in order to expand your ports?

Thanks for bringing up this topic.  I had not reviewed the Bus Pirate schematic in detail before now, or I would have pointed out the problem with the 5 V regulator.  Basically, the Bus Pirate needs to be redesigned with a 5 V boost regulator instead of a standard regulator.  Otherwise, as you point out, there is not much use in having a feature which could so easily fail to work properly, given the USB environment.
[/quote]

Well answered, thanks. I think it's a good idea considering the wide, unpredictable variety of "gimmicks" which are likely to be connected to BP...
Oh, it's going to be fun fitting an SMPS on that already "comfortably crowded" PCB ! Don't forget generous ground planes !

Re: Bus Pirate v4 hardware

Reply #92
[quote author="fenugrec"]Oh, it's going to be fun fitting an SMPS on that already "comfortably crowded" PCB ! Don't forget generous ground planes ![/quote]I think you may be the only one wanting to add an SMPS.  There is a separate DP project to create a PS, but that's not a BP.  I think it was you who suggested a PWM-controlled supply, but maybe that was someone else.

In any case, the MAX1595 only needs three small SMD caps, and it smaller than an 8-pin SOIC, so it can fit in almost the same space as the questionable 5V regulator.

Re: Bus Pirate v4 hardware

Reply #93
Thanks for your feedback, I read all your comments with great interest. There's always room for new stuff in the next hardware update.

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*VREGEN signal - that's just to turn on / off the regulators and save a few uA, right ?

It's not to save power, it's to switch the regulators off so everything is in a safe high-impedance state when the Bus Pirate starts up. The idea is that the BUs Pirate doesn't interact with a test circuit until specifically commanded to.

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*PUVSEL33 / PUVSEL50  signals - this is the selector to use either 3.3 or 5V ?

This is a new feature that's in development for v4. The v3 hardware fed the on-board pullup resistors from an external pin on the IO header. This confuses tons of people, so we added a high-side switches so a 3.3 or 5volt pullup can be selected from software. More about the on-board pullups:
http://dangerousprototypes.com/docs/Pra ... _resistors

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*VR3. This is the 5V regulator. What is its justification?
1. Enable-able ~5votl supply, 2. regulate USB over 5.0volts, 3. in practice its a cheap part that seems to work ok in this capacity. It should also (depending on part and SPECs) provide over-current, short-circuit, and over-heat protection.

The MAX1595 looks really interesting, and I'd be willing to try something like that. The MAX1595 is (according to shifty Maxim) $1.43 @ 1000. I could only find the msop8 version at Digikey for $4.05. Even at the 1000 price (remember, we only make 100s of Bus Pirates), it's 10x more expensive than the 5volt regulator.
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Re: Bus Pirate v4 hardware

Reply #94
[quote author="ian"]The MAX1595 looks really interesting, and I'd be willing to try something like that. The MAX1595 is (according to shifty Maxim) $1.43 @ 1000. I could only find the msop8 version at Digikey for $4.05. Even at the 1000 price (remember, we only make 100s of Bus Pirates), it's 10x more expensive than the 5volt regulator.[/quote]Point taken.  I have also suffered from the difficulty in obtaining Maxim parts, such as an RS-485 receiver that I ended up getting 9 free samples to meet my total needs.  But despite how cheap the Micrel part may be, it just won't work in all USB setups.

You might want to look into Linear, or maybe Texas Instruments.  I'm sure lots of companies make boost regulators for the USB world.  I recall considering Linear for my commercial design which used the MAX1595.  I looked at the LT1268 and LTC1157, but forget the prices.  It seems like Texas Instruments should have something to offer, but I do not recall any part numbers.  There has to be something that will work, even if you roll your own with the PWM on the PIC.

Re: Bus Pirate v4 hardware

Reply #95
[quote author="rsdio"]
I think you may be the only one wanting to add an SMPS.
[/quote]

Not specifically, I just wanted to remove the linear 5V reg - but you and Ian justified its presence, so I rest my case !
I indeed suggested the PWM driven supply to replace the secondary 3.3 regulator and provide more functionality. (That's also what lead me to the 5V questions)
Incidentally, it would also act as a switchable power supply : just set the PWM to 0% and the load is effectively off, the only current draw being the op-amp's quiescent current and the transistor leakage

Does any of you have an idea whether there's room in the software to add the PWM reg I've been rambling
on about ? I figure it would be pretty simple, but I'm not familiar with PICs > 18F .... Give me a 10F200 however and
I'll get it working in no time !

Re: Bus Pirate v4 hardware

Reply #96
There's a couple pin-assignable hardware PWMs in the pic24s :) The problem is going to be the extra pins though, but there's plenty of them on the V4.
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Re: Bus Pirate v4 hardware

Reply #97
I just had a thought.
The usb connector on the board actually has a footprint of mini-A/B.
Couldn't we then route the ID pin of the connector to the unused RP16/USBID pin of the PIC?
All other facilities i.e Vbus sensor/detector is already in place except for supply.
The supply could be taken care of by a "hacked" usb-otg cable.
Then there would be a future possibility of USB-OTG.
That could be used for rrreeeaaallllllyyy long BASIC scripts via external hard drive :-)
Or connect a hub, keyboard and the usb lcd backpack developed in another thread and then we have a handheld field testing device.
Firmware wanting of course.

But I would think it'll make the v4 hardware even more future proof.

Re: Bus Pirate v4 hardware

Reply #98
[quote author="honken"]The usb connector on the board actually has a footprint of mini-A/B.
Couldn't we then route the ID pin of the connector to the unused RP16/USBID pin of the PIC?[/quote]I would buy the Bus Pirate v4 just for such an OTG feature, because that would make it a cheaper PIC OTG evaluation board than anything Microchip offers.  Anyone interested in getting started with OTG programming but who doesn't want to design the initial hardware could use the BPv4 as a platform for early firmware development and testing.

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All other facilities i.e Vbus sensor/detector is already in place except for supply.
The supply could be taken care of by a "hacked" usb-otg cable.
I think it might be better to add a header pin to the BPv4 board so that external power can be applied directly, and then the OTG function could operate without a hacked cable.  OTG only needs to provide 100 mA, so it shouldn't be much of an issue.  This might be more complicated than I think, though.

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Then there would be a future possibility of USB-OTG.
That could be used for rrreeeaaallllllyyy long BASIC scripts via external hard drive :-)
Or connect a hub, keyboard and the usb lcd backpack developed in another thread and then we have a handheld field testing device.
Firmware wanting of course.
Yes, the PIC OTG host will only support the protocols that you program into the firmware.  There is no automatic hosting for OTG just because the hardware is there.  But having a cheap platform like the BPv4 would make it easier for the open community to start writing this sort of firmware.

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But I would think it'll make the v4 hardware even more future proof.
At the very least, the unused pin should be connected so that brave firmware developers can get started.  In other words, I think you have a great idea thought here, and a worthwhile suggestion.

Re: Bus Pirate v4 hardware

Reply #99
Completed board, except Q1 which is incorrectly designed. Will be testing this with Honken's USB stack ASAP :)
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Re: Bus Pirate v4 hardware

Reply #100
Cool! Looking forward for the results!

Re: Bus Pirate v4 hardware

Reply #101
Honken's USB stack is working on the IR Toy. I started to port it to 24F but there are unresolved issues. You can read about the stack and the 24F port here:
http://dangerousprototypes.com/forum/in ... 31#msg9331
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Re: Bus Pirate v4 hardware

Reply #102
By the way, the POV topic suggested using the resistor array from the BPv4 design, and that made me realize that I haven't seen the Eagle files for this yet, or even the BoM.  Have I just missed it somewhere?  (Hope this isn't the wrong topic to be asking - i.e. hope I'm not hijacking)

Re: Bus Pirate v4 hardware

Reply #103
The eagle files are back there somewhere. I have updated files though, that aren't quite done, I'll post them today probably.
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Re: Bus Pirate v4 hardware

Reply #104
Here's the latest board and eagle files.

Props if you can figure out a routing that lets us use a resistor array with the four resistors by the PNP transistors.

-Moved the LEDs closer to the board edge.
-Swapped MOSI and MISO text in the reference layer outside the board, I already swapped this last time (can't recall), maybe we used the old copy of the buspirate when we start to revise it.
-Change the resistor arrays with a much bigger landing pads. Added it also to dp_devices named RNETWORK.
-IO header chaged to shrouded PTH type
-USB ID pin (pin33) is now connected to USB mini-b. USB mini-b device on our dp_devices is also updated since the USB ID pin was not included in the symbol.
-AUX1 is now in included in port D. All AUX pins is now on port D
-external power header is included, I also added a diode in series
-3 10k Resistor array replaced some pull-ups exluding the MOSI and 8 voltage divider resistors on 5V and 3.3V sensors. I used the 0603-concave on 'resistor-dil' lbr.
-flipped the crystal to fit in 1 trace
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