ICD2 Variable VPP? - Electronic Circuits Projects Diagrams Free

Mike, K8LH · 30th June 2006, 08:17 PM

In the original ICD2 schematic MC uses an MCP41010 digital pot connected to the '877 RB1, RB6, and RB7 pins for the SPI interface and driving an MC34063 switching regulator.

Does the ICD2 really control the VPP voltage? If so, is there any reason you can think of that would prevent me from designing a little 8-pin 12F683 boost regulator with an SPI interface that would emulate the 256-steps of the digital pot to provide the same "variable VPP" function in a single circuit for my ICD2-USB clone design?

TIA, Mike

**Jay.slovak** · 30th June 2006, 08:44 PM

Hi Mike,

I am designing new ICD2 clone as well and I have been thinking about this too. Although I do have the MCP part on the shelf, I will replace it with a simple trimmer set to 12.5V (this value works the best for me). I used to program 18F with 13V without problems, so fixed VPP shouldn't be a problem.

EDIT: 12F683 emulating MCP + DC-DC booster is just not worth the effort IMHO

Mike, K8LH · 30th June 2006, 08:48 PM

Hi Jay,

So, what are you using to generate VPP?

Mike

**Jay.slovak** · 30th June 2006, 08:53 PM

Currently MC34063 but will switch to (simplier) MAX632.

Mike, K8LH · 30th June 2006, 11:37 PM

Ok, so you've got an IC and a trimmer (pot). That's cool.

I agree that it may be too much work/effort. If it could be done though, I think I'd prefer a single IC solution with ICD2 controlled variable VPP. Less board space, more control, great "cool" factor (grin).

Mike

William At MyBlueRoom · 1st July 2006, 04:56 AM

Quote:

Originally Posted by Mike, K8LH

In the original ICD2 schematic MC uses an MCP41010 digital pot connected to the '877 RB1, RB6, and RB7 pins for the SPI interface and driving an MC34063 switching regulator.

Does the ICD2 really control the VPP voltage? If so, is there any reason you can think of that would prevent me from designing a little 8-pin 12F683 boost regulator with an SPI interface that would emulate the 256-steps of the digital pot to provide the same "variable VPP" function in a single circuit for my ICD2-USB clone design?

TIA, Mike

Here's the MCP41010 in a ICD2 schematic from CZ...

Mike, K8LH · 2nd July 2006, 05:30 PM

Yes, I've seen that schematic Bill. Thanks.

I was thinking about something like the drawing below. A single chip that emulates the 256-step MCP41010 digi' pot and provides the variable boost VPP output voltage.

Regards, Mike

**Nigel Goodwin** · 2nd July 2006, 05:36 PM

Quote:

Originally Posted by Mike, K8LH

Yes, I've seen that schematic Bill. Thanks.

I was thinking about something like the drawing below. A single chip that emulates the 256-step MCP41010 digi' pot and provides the variable boost VPP output voltage.

Doesn't the PICKIT1 already do that to generate the 13V Vpp from the 5V USB voltage?.

Mike, K8LH · 2nd July 2006, 05:53 PM

Hi Nigel,

That PWM drive is right out of the PICKit2 schematic.

This circuit, if it can be done, would basically combine the function of the MCP41010 digital pot' and the MC34063 switching regulator from the original ICD2 design, all in a single IC. And, the ICD2 firmware is already set up to control it. Cool, huh?

Regards, Mike

**Nigel Goodwin** · 2nd July 2006, 06:00 PM

Quote:

Originally Posted by Mike, K8LH

Hi Nigel,

That PWM drive is right out of the PICKit2 schematic.

This circuit, if it can be done, would basically combine the function of the MCP41010 digital pot' and the MC34063 switching regulator from the original ICD2 design, all in a single IC. And, the ICD2 firmware is already set up to control it. Cool, huh?

Yep!, it certainly is!

William At MyBlueRoom · 2nd July 2006, 06:56 PM

Should'nt there be feedback? I think since the ICD2 uses a linear PS and a LM317 once the voltage is set that's that.
But with a boost converter you'll have to monitor the output somehow dynamically...

Mike, K8LH · 2nd July 2006, 07:30 PM

Please check out the original ICD2 schematic with MCP41010 and MC34063. The '877/A monitors the voltage via ADC and then adjusts the digi' pot. This should work, shouldn't it? Or should I consider 12F683 A2D PID loop to make it all that much more "bullet proof"?

Mike

**Jay.slovak** · 2nd July 2006, 08:18 PM

I would certainly add some sort of Feed-back to the 12F683 (and a suitable control algoritm). Without it, the generated voltage could change as the current draw changes.

Mike, K8LH · 2nd July 2006, 08:34 PM

Hi Jay,

Do you think it's worth putting the effort into the project? I'm still not sure how the ICD2 firmware utilizes that digital pot control function. Does it actually vary VPP voltage depending on Target device?

Regards, Mike

**Jay.slovak** · 2nd July 2006, 08:43 PM

Hi Mike,

As I already said "12F683 emulating MCP + DC-DC booster is just not worth the effort IMHO".

It is very little known about ICD2s control over Vpp. My guess is, each firmware sets it's own Vpp (12.5V for 18F, 12F for 12F683, whatever) and keeps it that way. I think the value is Hard-coded in the Firmware.

PS: Don't take me wrong. I think that 12F683 solution is elegant. I just don't think developing it for saving one IC and build only one or two ICDs is a waste of your (precious) development time. But, if you were to make a thousand ICDs, price savings could be significant.

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30th June 2006, 08:17 PM	(permalink)
Mike, K8LH	ICD2 Variable VPP? In the original ICD2 schematic MC uses an MCP41010 digital pot connected to the '877 RB1, RB6, and RB7 pins for the SPI interface and driving an MC34063 switching regulator. Does the ICD2 really control the VPP voltage? If so, is there any reason you can think of that would prevent me from designing a little 8-pin 12F683 boost regulator with an SPI interface that would emulate the 256-steps of the digital pot to provide the same "variable VPP" function in a single circuit for my ICD2-USB clone design? TIA, Mike

30th June 2006, 08:44 PM	(permalink)
Jay.slovak	Hi Mike, I am designing new ICD2 clone as well and I have been thinking about this too. Although I do have the MCP part on the shelf, I will replace it with a simple trimmer set to 12.5V (this value works the best for me). I used to program 18F with 13V without problems, so fixed VPP shouldn't be a problem. EDIT: 12F683 emulating MCP + DC-DC booster is just not worth the effort IMHO __________________ "I share, thus I am" Jay.slovak Read this! ICD2 Clone Best PIC/DsPIC Bootloader Read my Inchworm ICD2 review!

30th June 2006, 08:48 PM	(permalink)
Mike, K8LH	Hi Jay, So, what are you using to generate VPP? Mike

30th June 2006, 08:53 PM	(permalink)
Jay.slovak	Currently MC34063 but will switch to (simplier) MAX632. __________________ "I share, thus I am" Jay.slovak Read this! ICD2 Clone Best PIC/DsPIC Bootloader Read my Inchworm ICD2 review!

30th June 2006, 11:37 PM	(permalink)
Mike, K8LH	Ok, so you've got an IC and a trimmer (pot). That's cool. I agree that it may be too much work/effort. If it could be done though, I think I'd prefer a single IC solution with ICD2 controlled variable VPP. Less board space, more control, great "cool" factor (grin). Mike Last edited by Mike, K8LH; 1st July 2006 at 01:13 AM.

2nd July 2006, 05:53 PM	(permalink)
Mike, K8LH	Hi Nigel, That PWM drive is right out of the PICKit2 schematic. This circuit, if it can be done, would basically combine the function of the MCP41010 digital pot' and the MC34063 switching regulator from the original ICD2 design, all in a single IC. And, the ICD2 firmware is already set up to control it. Cool, huh? Regards, Mike

2nd July 2006, 06:56 PM	(permalink)
William At MyBlueRoom	Should'nt there be feedback? I think since the ICD2 uses a linear PS and a LM317 once the voltage is set that's that. But with a boost converter you'll have to monitor the output somehow dynamically... __________________ Bill Home of the Firefly PIC Tutor Inchworm ICD2 http://www.blueroomelectronics.com

2nd July 2006, 07:30 PM	(permalink)
Mike, K8LH	Please check out the original ICD2 schematic with MCP41010 and MC34063. The '877/A monitors the voltage via ADC and then adjusts the digi' pot. This should work, shouldn't it? Or should I consider 12F683 A2D PID loop to make it all that much more "bullet proof"? Mike Last edited by Mike, K8LH; 2nd July 2006 at 07:34 PM.

2nd July 2006, 08:18 PM	(permalink)
Jay.slovak	I would certainly add some sort of Feed-back to the 12F683 (and a suitable control algoritm). Without it, the generated voltage could change as the current draw changes. __________________ "I share, thus I am" Jay.slovak Read this! ICD2 Clone Best PIC/DsPIC Bootloader Read my Inchworm ICD2 review!

2nd July 2006, 08:34 PM	(permalink)
Mike, K8LH	Hi Jay, Do you think it's worth putting the effort into the project? I'm still not sure how the ICD2 firmware utilizes that digital pot control function. Does it actually vary VPP voltage depending on Target device? Regards, Mike

2nd July 2006, 08:43 PM	(permalink)
Jay.slovak	Hi Mike, As I already said "12F683 emulating MCP + DC-DC booster is just not worth the effort IMHO". It is very little known about ICD2s control over Vpp. My guess is, each firmware sets it's own Vpp (12.5V for 18F, 12F for 12F683, whatever) and keeps it that way. I think the value is Hard-coded in the Firmware. PS: Don't take me wrong. I think that 12F683 solution is elegant. I just don't think developing it for saving one IC and build only one or two ICDs is a waste of your (precious) development time. But, if you were to make a thousand ICDs, price savings could be significant. __________________ "I share, thus I am" Jay.slovak Read this! ICD2 Clone Best PIC/DsPIC Bootloader Read my Inchworm ICD2 review!