Search found 22 matches

by mooredan
Tue Oct 08, 2019 1:34 am
Forum: Hardware
Topic: Mystery 330 ohm resistor connected to X1
Replies: 4
Views: 460

Re: Mystery 330 ohm resistor connected to X1

Both of them are issue 3 "ISS 3". Both have red solder mask on the underside, but one has a white top silkscreen and the other has a yellow silkscreen. The silkscreen is virtually identical except the yellow one has the number 8243 near the oscillator circuit. Yeah, I figured as much, suspecting it ...
by mooredan
Mon Oct 07, 2019 2:54 am
Forum: Hardware
Topic: Mystery 330 ohm resistor connected to X1
Replies: 4
Views: 460

Mystery 330 ohm resistor connected to X1

Just doing a bit of backward engineering and I discovered that two of my ZX81 boards have a 330 ohm resistor (orange-orange-brown; front and center in the photos below) that isn't on the schematics. This resistor is connected to the node where X1 and C6 are connected. The other terminal is to ground...
by mooredan
Sat Dec 23, 2017 3:22 am
Forum: Hardware
Topic: Yet another ROM adapter
Replies: 46
Views: 7875

Re: Yet another ROM adapter

There ya go. ...looks great.
by mooredan
Sat Dec 23, 2017 1:55 am
Forum: Hardware
Topic: Yet another ROM adapter
Replies: 46
Views: 7875

Re: Yet another ROM adapter

... Coming back to your adapter, could you use all components in SMD packages including both capacitors in next revision of the board? MLCC 4.7uF/10V is available in 805 size. In KiCAD you can also find components' footprint for hand soldering. Pads are longer and they are really handy. Yes, they r...
by mooredan
Sat Dec 23, 2017 1:45 am
Forum: Hardware
Topic: Issue 3 16k internal RAM mod
Replies: 23
Views: 4520

Re: Issue 3 16k internal RAM mod

Kind of late to the party, but here's another completed mod (click on image for full size): https://s3-us-west-2.amazonaws.com/files.suncup.net/IMG_1395_sml.JPG https://s3-us-west-2.amazonaws.com/files.suncup.net/IMG_1396_sml.JPG No problem at all, here's the output of "PRINT PEEK 16388 + 256 * PEEK...
by mooredan
Fri Dec 22, 2017 2:22 am
Forum: Hardware
Topic: Yet another ROM adapter
Replies: 46
Views: 7875

Re: Yet another ROM adapter

...or just remove the ROM socket from the ZX81 board altogether and solder the adapter board directly in. If you can program an EPROM, there's really no need to ever have to remove the adapter -- that's what's the ZIF socket is for. Yeah the 0805 resistors are about the limit for comfortably solderi...
by mooredan
Thu Dec 21, 2017 8:51 am
Forum: Hardware
Topic: TI99/4A KEYBOARD ADAPTATION
Replies: 41
Views: 8434

Re: TI99/4A KEYBOARD ADAPTATION

Nice now don't forget decals for logo! Mooredan>> Still needs to be cleaned up a bit and I plan to cut up a junk ZX81 keyboard and glued the them onto the key caps -- but it doesn't look like the functions will fit -- may have to either exclude them or shrink them. I cut up a laser print of keyboar...
by mooredan
Thu Dec 21, 2017 8:47 am
Forum: Hardware
Topic: TI99/4A KEYBOARD ADAPTATION
Replies: 41
Views: 8434

Re: TI99/4A KEYBOARD ADAPTATION

That reminds me, I do plan on doing some debouncing mitigation on the keyboard. I seem to recall this sometimes showing its face. Here's a good reference: http://www.labbookpages.co.uk/electronics/debounce.html
by mooredan
Thu Dec 21, 2017 8:40 am
Forum: Hardware
Topic: Yet another ROM adapter
Replies: 46
Views: 7875

Re: Yet another ROM adapter

I should have used a right angle style jumper for the A13 line. ...and probably used two resistors, instead of one, on the A13 tie up/down. What are we looking at, 10 uA max through a 1kohm = 10mV drop --- yeah probably OK, but not having the resistor in the path would just make me feel better. Anyw...
by mooredan
Thu Dec 21, 2017 5:38 am
Forum: Hardware
Topic: Yet another ROM adapter
Replies: 46
Views: 7875

Re: Yet another ROM adapter

gamma, send me your paypal email address and I respond with an invoice. It's the last one available. Looks like there's enough interest to order another batch, ....but I'll wait for feedback for any potential design changes or improvements. I'm on the verge of routing a wire from A13 over to the jum...