Inchworm 1.5 reed relay mod (Switched +5V on Target)

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Evan is correct. The 18F4550 provides the USB-to-parallel connections to the parallel pins on the '877A that the obsolete Cypress chip had provided. Those parallel control connections are why the USB interface provides much improved debugger performance over the serial interface.
 
For what it's worth, William, if it were possible for you to make an ICD2 clone as you described that could be built as a serial model and upgraded to USB by adding the 18F4550 and related circuitry, I think that would be really cool, especially given the cost of the 18F4550 chips.

Since the USB model is using a parallel interface and the serial is not, there would obviously be some difference between the two, but perhaps they're compatible enough that you could manage to implement either interface with a single board layout.
 

It's in the works.
Might lose the 7805, and use the USB as 5v power. I do like the relay solution (optional) vs the pfet. I also want to use the DS411 to replace all the transistors.

It will be buildable as a stock inchworm
upgradable to the relay
and also to the 18F4550
 
blueroomelectronics said:
Opps DG411 is a quad analog switch.
Click to expand...

Oh! - it's NOT a very good idea then!, the original David Tait design used an analogue switch - but that was because he was a programmer, and NOT an electronics designer. The improved version used transistors, as have PIC programmer since.
 
I think it the same part used in the real ICD2, it replaces a handful of transistors and resistors and makes it slightly eaiser to assemble.
Attached is a clone schematic (with what appears to be an error on RA4 (no pullup) that uses an 16F877, 18F4550 and a DG411. The DG411 from the spec sheet looks ideal for the job, I'd like to change the configuration slightly to replace the transistor with the spare gate.
 

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  • ICD2 schematic 18F4550.pdf
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Probably OK if it's been sold as a kit?, but for sourcing the components yourself using an obscure IC probably isn't a good idea?.
 
Nigel Goodwin said:
Probably OK if it's been sold as a kit?, but for sourcing the components yourself using an obscure IC probably isn't a good idea?.
Click to expand...

When the Inchworm II is ready I'll be selling both, the original as the PCB only for about $17CDn and the Inchworm II as a kit, trying to keep it as close to the original kit price as I can $45CDn for the hobby grade. (RS232, no relay, USB powered) The DG411 is not that hard to source, and of course the original Inchworm was designed around very common parts. (hey no zeners or inductors)
 
So does the mod work? Has anyone tested it yet? If I am understanding this correctly, addition of the relay will make it possible to reprogram certain PICs after disabling the MCLR function, by switching the 5V line to the target PIC. And the reason you would disable the MCLR pin is to gain an extra I/O pin? Is there another reason?

Since I just assembled my kit, and have yet to program a PIC with it, I am in no hurry to get Inchworm II yet! I would however like to squeeze as much reliable functionality out of what I have.

Is the relay the best method? Are there other possible mods? Would it be feasible to modify for LVP?
 

Yes it works fine, do you need it not really. Most clones don't have the switched +5V.
As for LVP, you really don't want it. It wastes an I/O pin and has no real use if you have a HVP programmer.
 
Thanks William,

BTW, I got the firefly board and it is awesome! I'm going to start out with the ZIF only option for now, the parts are on the way.

From what I can see, only SW5-5 and 6 are needed right? I only have a 4 position DIP switch on hand. I intend on using a 14 pin low profile IC socket with two of the pins cut off for SW5 and plugging in my 4 position DIP such that SW5-3 thru 6 are hooked up. The socket will intrude ever so slightly on the pad for the stand-off, but I don't forsee any problems with that. At least then I can change it to a six position if I decide to populate the rest of the board.

Also, in the firefly assembly instructions parts list,and schematic (and the inchworm parts list, schematics and references) con5 (on the firefly) and con1 (on the inchworm) is reffered to as ICD when it should be IDC. I didn't even notice on the inchworm kit at first because everything came with it, however when I looked at the parts list to make an online order I had a hard time finding it at first.

EDIT: I just realised that this could be construed as negative criticism (spelling??). I am only trying to help. Your products and customer support are top notch, so keep up the good work!!
 
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Sig239 said:
Also, in the firefly assembly instructions parts list,and schematic (and the inchworm parts list, schematics and references) con5 (on the firefly) and con1 (on the inchworm) is reffered to as ICD when it should be IDC.
Click to expand...
but... the inchworm is an in-circuit debugger (ICD), and that connector is the one through which it debugs the target board - so it seems appropriate to call it the ICD connector - even if it's a pretty big coincidence that the actual physical style of connector involved is IDC
 

I would just tack solder a small link over the 40 or 18 link depending on which PIC I was going to start with. Easier than opening the holes later if you decide to build the "Fly" half when you get a 6 position DIP switch.
 
blueroomelectronics said:
I get some flac over the correctly labeled DE9. DB means 25 shell.
Click to expand...
Where'd you see that convention? From everything I've seen, DB is just short for "D-subminiature" which just refers to the D-shape of the connector. DB9, DB15, DB25, DB37 - all names I've seen used frequently and I don't recall ever seeing them named with "DE"...
https://www.cablestogo.com/resources/db.asp
 
blueroomelectronics said:
I would just tack solder a small link over the 40 or 18 link depending on which PIC I was going to start with. Easier than opening the holes later if you decide to build the "Fly" half when you get a 6 position DIP switch.
Click to expand...
Opening what holes? I will just take the 4 postition DIP switch out of the IC socket and put in a 6 position DIP switch.
 

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  • DIPinSocket.JPG
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