Skip to main content
Topic: PicProgrammer v2 for BusPirate v4 Development (Read 38555 times) previous topic - next topic

Re: Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #15
Hopfully im not imposing on any current convos or reasking a question already awnsered. but I read somwhere (or thought anyways) that Ian had plans to order ~100 and put the programmers back into production, or atleast a fun run :D

Im just wondering if this can be confirmed and if so, is there a date set (ima mark my calender)

Also out of curiosity and if so; Are we going to be seeing a new revision on the first? perhaps with some of the 'maybe not now but future' design considerations?

Oh and also; what version BP will it be for? Now that BP 4 has different pin configuration. I have both so ill be good ;P

Re: Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #16
I will talk about this in todays video blog too :) Yes, ordering 100. Need to get a different connector due to Ian-stupidity, so I have not actually ordered the production yet. It will be the same as the original and v3 only, no part updates.
Got a question? Please ask in the forum for the fastest answers.

Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #17
Today I looked at Ladyada's boost converter tutorial (has a nice calculator for values), did some fiddling around and liked these values for input:
- Frequency: 125 kHz (We use 16MIPS, this gives us 7 bit resolution for duty cycle, the bigger, better for inductor size)
- Min Vin: 4V (We will use 5V input, this is the minimum USB supply)
- Max Vin: 5V (We might get this, but usually sth like 4.9V)
- Min Vout: 8V (Giving some head room, low power pics require 8.5V, right?)
- Max Vout: 18V (Some max value I close, we can do with lower voltages maybe?)
- Iout: 0.01Amps (This is a bit over estimation, but bigger, the better for inductor size. We also include feedback voltage divider current here)
- Vripple: 0.1V (Affects output cap value)

The results I got were:
- Min. Duty Cycle: 37.5%
- Max. Duty cycle: 77.777%
- Min. Inductor size: 468.75 uH (Will get a 470 uH inductor)
- Peak inductor current: 0.062 A (Found a 0.9A inductor, perfect!)
- Minimum capacitor: 0.7999 uF (So, 1uF is enough)
- Minimum Schottky diode: 18V 0.062 A

So the parts I'll get are:
- 470uH, 0.9A inductor
- 100V 1A Schottky diode

Now have to figure out a transistor, I'm thinking an NPN transistor like this.

Any ideas or suggestions before I go shopping on weekend? :) I'll breadboard it and give you some results hopefully by the weekend.

Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #18
Most switching powersupplies use a fet. As I understand (but i'm a digital guy) these have a small on resistance.

You are going to akihabara? :D

Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #19
[quote author="Sjaak"]You are going to akihabara? :D [/quote]

hah, i was thinking the same thing. If you ask me; Akihabra is like cheating. :D You should have to order by mail and wait like the rest of us :D

 

Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #20
offtopic: I was just asking because I did forget to get something over there :)

These parts you can also obtain easily at your local electronics shop.

Re: Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #21
even further off-topic: :( I dont have any electronic parts store that i know of near me. there is a nice size reseller right next to me but they dont have a store; which sucks.

Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #22
[quote author="Sjaak"]Most switching powersupplies use a fet. As I understand (but i'm a digital guy) these have a small on resistance.[/quote]
That's totally true, they use MOS-FETs. But this being a prototype I guess I can do with an NPN transistor. In that tutorial, there is a IRFD110 (N-ch MOS-FET)driven directly by a uC pin, which is weird, usually you have to use some sort of driver IC or sth. I can try the same thing once I have a little time to look at that schematic (just came back from hackerspace).

[quote author="Sjaak"]You are going to akihabara? :D [/quote]
Of course, where else I'll get my parts in short time? :)

[quote author="BrentBXR"]hah, i was thinking the same thing. If you ask me; Akihabra is like cheating. :D You should have to order by mail and wait like the rest of us :D[/quote]
I do that too, some parts are not found in Akihabara (especially some SMD stuff) so I use Digikey, Mouser etc too. :) But for most shopping there is Akihabara. :D

Re: Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #23
We also have a parts order going out tomorrow, if I can add anything small to it.

Usually SMPS is with a FET, but I have done it with a NPN too (less current available though).

I would use a 3-10uF tantalum for the cap.
Got a question? Please ask in the forum for the fastest answers.

Re: Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #24
I guess I'll try some local parts here and breadboard the design first. Later we can organize sth for the prototypes maybe.

I checked out the available FETs, here are they for price etc comparison (they have pdf datasheets too):
- 2SK2232 with Vth = 0.8-2.0V
- 2SK2936 with Vth = 1.5-2.5V
- PJP75N75 with Vth = 1.0-3.0V
- 2N7000 with Vth = 0.8-3.0V
- 2N7002K with Vth = 1.0-2.5V (SMD!)

I really liked the 2N7000 and 2N7002K ones, they are small and cheap! I'm adding those to my shopping list.

Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #25
[quote author="tayken"]In that tutorial, there is a IRFD110 (N-ch MOS-FET)driven directly by a uC pin, which is weird, usually you have to use some sort of driver IC or sth.[/quote]
What do you mean? I drive the gate of FETs with a PIC I/O pin all the time. As long as the gate on threshold is positive, you don't need any interface, not even a current-limited resistor. The challenge is for an FET that requires a negative gate voltage.

EDIT: I just grabbed the IRFD110 data sheet, and VGS(th) is minimum 2 V, maximum 4 V, so as long as your uC is running 5 V I/O outputs then you should have no problem driving the Power MOSFET directly.

Re: Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #26
It was my first time seeing sth like this. I just used FETs in university and they always wanted us to use some driver IC, I guess the threshold voltage was higher than 5V for those ones.

OK, so I'm fine with the above selections. There were some with max 4V, which got eliminated pretty quickly. Last two are my favorite, will try them when I get the chance.

Re: Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #27
For eg. a nixie tube power supply with 180V out, usually the FET needs >5volts (at least >3.3volts), for small stuff like this though we have a few more options in the logic level range.
Got a question? Please ask in the forum for the fastest answers.

Re: Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #28
Plus voltage and current ratings are enough too: Both have Vdss as 60V and Id 200mA and 300mA respectively. I don't know what else to check, all the values seem fine to me.

Re: Where to got a PicProgrammer adapter for BusPirate?

Reply #29
Just try it :)