PCB for Microchip PIC14

[DavidMS]

As a bit of sideline while I get the things sorted to build my replica Mk14, I thought I would give the PIC14 a go. It looks like the info in EasyEDA is readily available for a slightly updated version but I just wanted to check before I placed a PCB order, that this is the best way to go for a PIC14 type board

[Phil__G]

Hi David, first you need to decide which version - the smaller PIC16F876 PCB is really cute and pocket-size handy, but Philloupat's larger PIC16F877 version is more MK14 sized and has all the flags brought out for experimenting with I/O - in addition to the obvious LEDs mine has driven servos, 240v solid-state relays, speakers... which you cant so readily do with the small one. But the small one is so cute! Both have a serial loader. The obvious answer is to build one of each!

[DavidMS]

Originally Posted by Phil__G

Hi David, first you need to decide which version - the smaller PIC16F876 PCB is really cute and pocket-size handy, but Philloupat's larger PIC16F877 version is more MK14 sized and has all the flags brought out for experimenting with I/O - in addition to the obvious LEDs mine has driven servos, 240v solid-state relays, speakers... which you cant so readily do with the small one. But the small one is so cute! Both have a serial loader. The obvious answer is to build one of each!

I need to have a look a Philloupat's version, but as you say to obvious solution is to build both !

[SiriusHardware]

DavidMS, I have a bare unbuilt 'Philoupat' PIC14 PCB which its creator kindly gave me in exchange for one of the first batch of MK14 issue VI PCBs.

It is the second version of his PIC14 PCB shown from post #9 onwards of this now closed thread, and it uses a 40-pin PIC16F877 so it does emulate the limited I/O of the SC/MP itself (but not the 16 lines of the RAM / I/O IC).

https://www.vintage-radio.net/forum/...d.php?t=166631

I already have a more compact PIC14 90% built, so I would be glad to pass this PCB on to you if you would like it. PM me if interested.

[SiriusHardware]

You might also be interested in the comprehensive feature updates added by forum member George60 (who we sadly haven't heard from for a while) later in that thread.

[Michael - K8LH]

May I impose to ask if anyone has the Gerber files for the PIC14 PCB that uses the 40-pin PIC, please? The schematic I have is labeled picv4.pdf.

TIA. Stay safe. Cheerful regards, Mike, K8LH (Michigan, USA)

[Mark1960]

Originally Posted by Michael - K8LH

May I impose to ask if anyone has the Gerber files for the PIC14 PCB that uses the 40-pin PIC, please? The schematic I have is labeled picv4.pdf.

TIA. Stay safe. Cheerful regards, Mike, K8LH (Michigan, USA)

I think it was the attachment on this post, or check the rest of that thread for a possible later version.
https://www.vintage-radio.net/forum/...7&postcount=76

[SiriusHardware]

The version I'm sending off to DavidMS later does have some minor physical (but not circuit) errors which are detailed in the thread, mainly to do with the physical placements of the power socket, serial-TTL converter module and extension connector. This was Philoupat's summary:-

the 9v plug is upside down.
the extension plug is too far from the edge.
the ft232 module must move forward but nothing that cannot be corrected

Otherwise, that version of the PCB works well.

[Phil__G]

Hi Mike, hope you're doing ok
Using PCBway's online gerber viewer I checked the attached file against my own PIC14 and its identical.
My PCB came directly from Philoupat so I think this is the 'current' version (16/05/2020) - the CH340G usb module (between the crystal and Q9) is 'a bit central' by maybe half an inch but works fine. Theres a switch to set (a define) in the source to say whether the intel hexloader is started by default. If enabled (mine is), then a 'SC/MP reset' is required to bypass it.

[DavidMS]

Originally Posted by SiriusHardware

DavidMS, I have a bare unbuilt 'Philoupat' PIC14 PCB which its creator kindly gave me in exchange for one of the first batch of MK14 issue VI PCBs.

It is the second version of his PIC14 PCB shown from post #9 onwards of this now closed thread, and it uses a 40-pin PIC16F877 so it does emulate the limited I/O of the SC/MP itself (but not the 16 lines of the RAM / I/O IC).

https://www.vintage-radio.net/forum/...d.php?t=166631

I already have a more compact PIC14 90% built, so I would be glad to pass this PCB on to you if you would like it. PM me if interested.

I'm pleased to say my PIC14 (thanks again to SiriusHardware for the PCB) came to life this morning. As I had some 4 digit bubble displays not doing anything I have used them for the display until I can find a sensibly priced calculator to take apart. As you can see I have modified the power connection slightly to provide for a micro USB.

Now I guess I need to try and program something....

[SiriusHardware]

Nice to see it working David, I'm glad it has found a good home.

I think that display would be fine as-is if you could find a red filter the exact size of the overall display assembly - does anyone know where to find those strips of stiff red plastic filter sheet nowadays?

I know what you mean about the way the price of common or garden basic LED calculators seems to have taken off - I have a Texet 880 here, one of several I bought for no more than £3-£4 a couple of years ago with a view to it being a potential display donor but this remaining one is in such immaculate condition that I wouldn't have the heart to dismantle it for its display. The others were all damaged in some way, keys missing, overlay dented, battery cover missing and priced accordingly so I didn't feel too bad about repurposing their displays, one of which is on my issue VI replica now.

[Phil__G]

Originally Posted by DavidMS

As you can see I have modified the power connection slightly to provide for a micro USB.

Theres provision for a CH340G USB module to the left of the crystal David - not only for power but also permits Intel hex upload
However I've noticed a bit of an anomaly which I've not dug into yet: The Intel hexloader works fine, but doesnt save like manually entered programs do.
Karen used spare PIC registers in 4 banks in combination with flash to give 256 bytes of non-volatile memory, and all SC/MP writes to memory also update these registers appropriately, so a program is retained during power-off. The hexloader seems to do writes to ram but not to the flash so although it works fine, hexloaded programs are not retained during power-off, and, IIRC, a PIC reset clears a hexloaded program. At least on mine anyway! I am looking at it but its one of many projects atm.
Another PIC14 will be born soon, the smaller one - a pal 'Wiggles' has asked for a programmed 876...

[Slothie]

Originally Posted by Phil__G

However I've noticed a bit of an anomaly which I've not dug into yet: The Intel hexloader works fine, but doesnt save like manually entered programs do.

I beleive the "non-volatile" function only applies to bytes set by the SCIOS monitor code (IE stuff you key in), so anything written by the hex loader or a user program does not get saved to EEPROM (because if it did, updates to variables would quickly "wear out" the EEPROM).

[Phil__G]

Its been over a year since I looked at this and I've forgotten how far I got but I think it might be the inability to write EEPROM at serial speeds (9600) thats the reason Karen didnt store hexloaded programs - its not EEPROM longevity - from the datasheet "The EEPROM Data memory is rated for high erase/write cycles (specification D120) ... EEPROM data memory can be used to store frequently updated values." I'll have to have another look & try to remember where I got to... the nonvolatile thing is brilliant, especially for demos, but you cant be keying everything in manually....
Maybe try to follow up a hexload with EEPROM block write rather than a received byte at a time.

[Slothie]

Originally Posted by Phil__G

Its been over a year since I looked at this and I've forgotten how far I got but I think it might be the inability to write EEPROM at serial speeds (9600) thats the reason Karen didnt store hexloaded programs - its not EEPROM longevity - from the datasheet "The EEPROM Data memory is rated for high erase/write cycles (specification D120) ... EEPROM data memory can be used to store frequently updated values." I'll have to have another look & try to remember where I got to... the nonvolatile thing is brilliant, especially for demos, but you cant be keying everything in manually....
Maybe try to follow up a hexload with EEPROM block write rather than a received byte at a time.

That would make sense. Although I think that one of George60's changes allowed you to save the contents of the RAM to Program storage, and retrieve it again later which might be another option.

[SiriusHardware]

If you were desperate to make hexloaded programs 'stick' then one of the keypad entry uploaders would do it because they enter the code using keystrokes the way a human operator would, although I don't think the PIC14 boards have a convenient external keypad connector like the full scale replicas do.

[DavidMS]

Originally Posted by Phil__G

[Theres provision for a CH340G USB module to the left of the crystal David - not only for power but also permits Intel hex upload Another PIC14 will be born soon, the smaller one - a pal 'Wiggles' has asked for a programmed 876...

Yes, I realised there was a option to add a USB module, I may in the future but was looking to get up and running with bits I had around the workshop just too excited to get going

If you are looking to re-lay the PCB might I suggest adding a PIC in-circuit programming connection so a PICKIT can easily be connected. It might need a jumper to disconnect the display from PGC & PGD if the loading upsets the programming

[Slothie]

Originally Posted by DavidMS

If you are looking to re-lay the PCB might I suggest adding a PIC in-circuit programming connection so a PICKIT can easily be connected. It might need a jumper to disconnect the display from PGC & PGD if the loading upsets the programming

I did this on mine the belt-and-braces way! My PIC14 had a plug in display, so i just unplugged it to isolate it.

[SiriusHardware]

I think you would have to appeal to Philoupat83 to get that change officially made but unfortunately he has not visited the forum (or at least not posted) for quite a while now.

...Unless Phil posted the design files for his current design as well as the gerbers?

[DavidMS]

Originally Posted by SiriusHardware

I think you would have to appeal to Philoupat83 to get that change officially made but unfortunately he has not visited the forum (or at least not posted) for quite a while now.

...Unless Phil posted the design files for his current design as well as the gerbers?

I think they have been posted, but I need to do a bit of digging as they are labeled as Kicad but look far more like Eagle