MK14 (Microcomputer Kit 14) PIC14
 

Hello
I realized the circuit pic14 an emulation of the celebre mk14 it works. for Karen's Corner pic14
http://www.techlib.com/area_50/Readers/Karen/micro.htm
and emulation mk14
http://www.dougrice.plus.com/dev/seg_mk14.htm

The quartz can be 4 mhz or 20 mhz I would want to load(charge) a program by the serial entrance(entry) with a converter usb
But it does not work made you tests how load has to leave the pc
thank you

Re: MK14 (Microcomputer Kit 14) PIC14
 

Bonjour Philoupat,

Ma Francais est terrible, mais je vais essayer.

Apres application de 5V, ou apres pression de 'PIC Reset', le PIC14 ecout l'entree serie pour un fichier Intel hex.

Le crystal doit etre 20 MHz. Si non, le baud rate (9600 8N1) sera faux.

J'espere que cet vous aide,

KarenO

Re: MK14 (Microcomputer Kit 14) PIC14
 

Hello KAREN
Thank you actually it works With a quartz 20mhz
I use a converter usb ttl and the Tera term software
the sending of files HEX is good
you think of a version USB RX TX ?
The version with the PIC 16F877 works?
Thank you again for your advice

Re: MK14 (Microcomputer Kit 14) PIC14
 

Hello again Philoupat,

Your English is much better than my French so I'll reply in English :)

I have no plans to add a USB socket to my PIC14 but there is a good alternative. The FTDI company sell USB serial leads where the adapter chip is embedded in the USB connector. FTDI lead number TTL-232R-5V-AJ has a USB plug one end (to plug into a computer) and a 3.5mm stereo plug at the other. The 3.5mm plug carries 5V level serial data: the tip is data FROM the computer, the ring is data TO the computer (which you don't need in this case), and the sleeve is ground. This makes it very easy to add a serial link to a microcomputer.

You will need to connect the tip contact of a 3.5mm socket to pin 6. You don't need the transistor because the levels are already the right way round. As a precaution, I would add a schottky diode so that nothing is stressed if the computer is switched on when the PIC14 isn't (see diagram 1).

I notice that your PCB uses transistors to drive the digits. Today I would recommend using a 74AC240 IC instead. The problem with transistors is that they don't switch off quickly, and this causes 'ghosts' to appear on the display when you run some of the example programs in the Mk14 handbook.

I am sorry about this but there is a solution - put a 10nF capacitor over each base resistor as shown in diagram 2. These capacitors will speed up the transistor switch-off and cure the ghost problem. So as not to spoil the appearance of your PCB, you could solder the extra capacitors to the under side.

I hope all this helps.

Re: MK14 (Microcomputer Kit 14) PIC14
 

Hi fellow Mk14 afficionados, and especially to Karen whose PIC14 is a great design as noted on this thread. A Google search brought me to another (now closed thread) on Vintage Radio about the Mk14, and found some comment about myself there. I run (and I use that word very loosely) the mymk14.co.uk website about my Mk14 adventures. I've not passed away - just resting / very busy with the rest of my life. You can find my latest updates on Twitter - @mk14man, although I do hope to get back and update (and indeed finish) my website. I do plan on doing more Mk14 things, like finishing the AVR based Mk14 clone, but need to find the time. I'm adding a picture it in the interim - hardware all done, bootloader & flash programmer done, main software not done!

Re: MK14 (Microcomputer Kit 14) PIC14
 

Hello Mk14man, yes, that was me wondering where you had got to in the other thread - nice to know you are still about - your website remains the go-to resource for all things MK14 related.

I'm in the process of building one of Karen's PIC based emulators myself in order to minimise wear and tear on my actual MK14, although I keep putting off the chore of wiring up the keypad. A task for the dark winter nights, hopefully.

Re: MK14 (Microcomputer Kit 14) PIC14
 

I know I'm a bit late to this party, but if you use a 74ACT240 to drive the cathodes, since it has totem pole output drivers aren't you in risk of shorting the power supply if two keys on different columns get pressed simultaneously? Or does the ACT series limit current? I'm afraid my knowledge of TTL kind of stopped with LS gates :)

Re: MK14 (Microcomputer Kit 14) PIC14
 

I remember noticing that the '240 didn't appear to have open collector outputs (as the original discrete transistor cathode drivers obviously did) but my PIC14 still doesn't have a keypad wired to it so I can't (yet) replicate the scenario you suggest to see if it has any repercussions in practice.

As it happens I can't think of any of the original example programs which required you press more than one key so this situation would rarely come up, but you are right to wonder what could happen. A two-finger typist might occasionally still be releasing one key as they hit another with the other finger.

Perhaps for anyone building one now, Karen's 'Third Way', retaining the transistors but adding capacitors would be the way to go.

Re: MK14 (Microcomputer Kit 14) PIC14
 

It's maybe a year later but is there any chance of a link to Karens '3rd way' or the PCB files (eagle or Kicad) for the MK14 emulator, maybe even a link to where the PCB could be purchased please.

Re: MK14 (Microcomputer Kit 14) PIC14
 

I'm not aware of any such files - Karen, as the creator, would be able to tell you better but I think all that was required was to add capacitors across the base resistors of the driver transistors in Karen's original circuit using discrete transistors rather than the 74ACT240 buffer proposed later. The whole project is quite easily built on stripboard, although manually wiring up the strange keypad matrix adopted by SOC is a bit of a chore, I admit.