after a few hours of sleep I was able to read the schematics again.
Q1 is 2N3906 and Q2 is 2N3904.
So I will finish my soldering this evening and give it a try.
Paul
New ZX80 boards
Re: New ZX80 boards
Hi all,
after a few hours of sleep I was able to read the schematics again.
Q1 is 2N3906 and Q2 is 2N3904.
So I will finish my soldering this evening and give it a try.
Paul
after a few hours of sleep I was able to read the schematics again.
Q1 is 2N3906 and Q2 is 2N3904.
So I will finish my soldering this evening and give it a try.
Paul
In theory, there is no difference between theory and practice. But, in practice, there is.
Re: New ZX80 boards
Hello all,
I'm still building my own ZX80 board; Sirmorris and Superfo are ahead of me! But I'm writing a manual as I go. Documentation takes time
On the vertical roll: I have had this problem with other old computers when used on new TV sets. The Sinclair ZX80 design "cheats" on the video standards, and does not produce the right frequencies. I think the new TVs assume perfect vertical and horizontal sync frequencies, so their lock-in range is small. Many do not even have Vertical Hold or Horizontal Hold controls any more. This may be the problem.Or it might be that we can play with the resistors that set the video and sync amplitudes to improve it.
To Sirmorris: HC logic should work just as well (even better) than LS logic. However, the input and output characteristics are different. HC inputs draw no current, and their outputs go right to 0v and 5v when lightly loaded. This might affect performance where Sinclair's design depended on the characteristics of LS parts. I redesigned the crystal oscillator to require the HC part, as they work much better as oscillators. But I would not be surprised if the RC networks (R2-C9, R24, R25-C11, R35-C14) need minor changes with HC parts.
On the keyboard problem: I built my board with LS parts like the original Sinclair ZX80. What I see in testing is that the low outputs of U10 are 0.3v or more, the diodes D3-D10 have a 0.6v drop or more, so the inputs of U10 are at 0.81 to 0.87v when a key is pressed. That is above the TTL low specification. I bought some germanium diodes to use at D3-D10 but have not had time to try them yet.
To Paul: Oops! Sorry to have missed sending Q2! It is a 2N3904. I can mail it if you don't already have one. It is also not critical; a 2N2222, 2N4401 etc. will also work.
Let's see... anything else I missed?
I'm still building my own ZX80 board; Sirmorris and Superfo are ahead of me! But I'm writing a manual as I go. Documentation takes time
On the vertical roll: I have had this problem with other old computers when used on new TV sets. The Sinclair ZX80 design "cheats" on the video standards, and does not produce the right frequencies. I think the new TVs assume perfect vertical and horizontal sync frequencies, so their lock-in range is small. Many do not even have Vertical Hold or Horizontal Hold controls any more. This may be the problem.Or it might be that we can play with the resistors that set the video and sync amplitudes to improve it.
To Sirmorris: HC logic should work just as well (even better) than LS logic. However, the input and output characteristics are different. HC inputs draw no current, and their outputs go right to 0v and 5v when lightly loaded. This might affect performance where Sinclair's design depended on the characteristics of LS parts. I redesigned the crystal oscillator to require the HC part, as they work much better as oscillators. But I would not be surprised if the RC networks (R2-C9, R24, R25-C11, R35-C14) need minor changes with HC parts.
On the keyboard problem: I built my board with LS parts like the original Sinclair ZX80. What I see in testing is that the low outputs of U10 are 0.3v or more, the diodes D3-D10 have a 0.6v drop or more, so the inputs of U10 are at 0.81 to 0.87v when a key is pressed. That is above the TTL low specification. I bought some germanium diodes to use at D3-D10 but have not had time to try them yet.
To Paul: Oops! Sorry to have missed sending Q2! It is a 2N3904. I can mail it if you don't already have one. It is also not critical; a 2N2222, 2N4401 etc. will also work.
Let's see... anything else I missed?
Last edited by Lee Hart on Sat Jul 03, 2010 1:53 am, edited 1 time in total.
Re: New ZX80 boards
Hi all,
just in case you'd like to know:
my ZX80 is ready and it's working. Does that make it serial# 3?
The keyboard works without problems, I used schottky diodes instead of 1N4148 for the keyboard.
There is a tiny problem with the display:
Every displayed line begins with pixel line #2, followed by #3 to #8, then line #1.
I try to append a photo.
Does anybody know what's the problem and how to fix it?
Thanks in advance
Paul
P.S: I would like to thank Lee so very much for his work. He did a great job. I never saw a ZX80-board more beautiful then this one!
Has anybody any idea for the case? Can anybody provide a negative of a ZX80-case for copying it with polyester?
just in case you'd like to know:
my ZX80 is ready and it's working. Does that make it serial# 3?
The keyboard works without problems, I used schottky diodes instead of 1N4148 for the keyboard.
There is a tiny problem with the display:
Every displayed line begins with pixel line #2, followed by #3 to #8, then line #1.
I try to append a photo.
Does anybody know what's the problem and how to fix it?
Thanks in advance
Paul
P.S: I would like to thank Lee so very much for his work. He did a great job. I never saw a ZX80-board more beautiful then this one!
Has anybody any idea for the case? Can anybody provide a negative of a ZX80-case for copying it with polyester?
In theory, there is no difference between theory and practice. But, in practice, there is.
Re: New ZX80 boards
Paul wrote:
> My ZX80 is ready and it's working. Does that make it serial# 3?
Wonderful! Yes, it is #3.
> The keyboard works without problems, I used schottky diodes instead of 1N4148 for
> the keyboard.
Be sure to check it with the shift key, too. Shift is where the problem was noticed on the other boards. If the keys still work shifted, then it's a good bet that the diode drop I mentioned is the problem.
> There is a tiny problem with the display: Every displayed line begins with pixel
> line #2, followed by #3 to #8, then line #1.
Do you have a jumper installed at P1 between pin 5-6 (TXD to RST)? This connects the CLR signal to U15B, the line counter. If this jumper is in place, check D11, D12, D14, Q1, R36, R37, and R38.
> My ZX80 is ready and it's working. Does that make it serial# 3?
Wonderful! Yes, it is #3.
> The keyboard works without problems, I used schottky diodes instead of 1N4148 for
> the keyboard.
Be sure to check it with the shift key, too. Shift is where the problem was noticed on the other boards. If the keys still work shifted, then it's a good bet that the diode drop I mentioned is the problem.
> There is a tiny problem with the display: Every displayed line begins with pixel
> line #2, followed by #3 to #8, then line #1.
Do you have a jumper installed at P1 between pin 5-6 (TXD to RST)? This connects the CLR signal to U15B, the line counter. If this jumper is in place, check D11, D12, D14, Q1, R36, R37, and R38.
Re: New ZX80 boards
Thanks for your reply, Lee.
Yes, the keyboard works with all shifted keys as well. So the diode drop was the problem (or my configuration works for any other reason).
We will know for shure if superfoe or SirMorris replaces the diodes and this solves their problem.
No, there was no jumper installed at P1 between pin 5-6 (TXD to RST). Thanks for the quick solution.
The only jumpers I installed at P1 were VI-VO and SI-SO (they sounded logical to me).
Should I install any other jumpers at P1?
My eprom programmer didn't like the 27128 (it was empty, but could not be programmed). So I used a AT28C64B instead.
I left W5 open, is that correct?
I also have some AT28C256B, I want to use that for switching between ZX80 and ZX81 Roms, but first I have to solder an adapter with jumper for Pin 1 to do the switching. Might this be a possible enhancement for the issue2 board?
I decided to solder U4 on the component side to have it look even closer to the original. But the pins of C8 seem to be very close, so it doesn't look save to install a heat sink. Maybe for issue2-boards, there could be a slightly lager gap (or an axial type for c8 with ground near the heat sink)?
Yes, the keyboard works with all shifted keys as well. So the diode drop was the problem (or my configuration works for any other reason).
We will know for shure if superfoe or SirMorris replaces the diodes and this solves their problem.
No, there was no jumper installed at P1 between pin 5-6 (TXD to RST). Thanks for the quick solution.
The only jumpers I installed at P1 were VI-VO and SI-SO (they sounded logical to me).
Should I install any other jumpers at P1?
My eprom programmer didn't like the 27128 (it was empty, but could not be programmed). So I used a AT28C64B instead.
I left W5 open, is that correct?
I also have some AT28C256B, I want to use that for switching between ZX80 and ZX81 Roms, but first I have to solder an adapter with jumper for Pin 1 to do the switching. Might this be a possible enhancement for the issue2 board?
I decided to solder U4 on the component side to have it look even closer to the original. But the pins of C8 seem to be very close, so it doesn't look save to install a heat sink. Maybe for issue2-boards, there could be a slightly lager gap (or an axial type for c8 with ground near the heat sink)?
In theory, there is no difference between theory and practice. But, in practice, there is.
Re: New ZX80 boards
Excellent!
My board has sprung back to life - I think I might have a dry joint - so next I'll be replacing some diodes! What part number are you using?
c
My board has sprung back to life - I think I might have a dry joint - so next I'll be replacing some diodes! What part number are you using?
c
Re: New ZX80 boards
Hi SirMorris,
I'm using BAT41. It took me a quarter of an hour to find this out. I had to use the power of two magnifying glasses
It is 100V 100mA. The voltage drop of mine were between 291mV and 316mV. The datasheet lists them with 0.4V
But I didn't select them. I just went to my local electronics dealer and asked for schottky diodes replacing 1N4148.
I'm glad they work so good.
I tried to save and reload programs, but I did not succeed. I tried using a ghetto blaster, but the signal comming out of the mic is very low. My pc also didn't recognise any signal. I will have to use my scope for a closer look.
For the keyboard cover I use a layout fond on the pages of Grant Searle
http://home.micros.users.btopenworld.co ... %20overlay
I printed it at a rate of 17%, which is very close to the size of our keyboard. Then I laminated it with 80 mic plastic (hot) which makes it a shiny "hard" cover. You can feel the buttons underneath.
Paul
I'm using BAT41. It took me a quarter of an hour to find this out. I had to use the power of two magnifying glasses
It is 100V 100mA. The voltage drop of mine were between 291mV and 316mV. The datasheet lists them with 0.4V
But I didn't select them. I just went to my local electronics dealer and asked for schottky diodes replacing 1N4148.
I'm glad they work so good.
I tried to save and reload programs, but I did not succeed. I tried using a ghetto blaster, but the signal comming out of the mic is very low. My pc also didn't recognise any signal. I will have to use my scope for a closer look.
For the keyboard cover I use a layout fond on the pages of Grant Searle
http://home.micros.users.btopenworld.co ... %20overlay
I printed it at a rate of 17%, which is very close to the size of our keyboard. Then I laminated it with 80 mic plastic (hot) which makes it a shiny "hard" cover. You can feel the buttons underneath.
Paul
In theory, there is no difference between theory and practice. But, in practice, there is.
Re: New ZX80 boards
Diodes D3-D10: I bought 1N270 germanium diodes from http://www.jameco.com (where I got almost all the other parts). Not the best price, but it's handy to get everything from one vendor to save shipping and handling charges.
Germanium diodes have about a 0.25v forward drop. Schottky is around 0.35v, and regular silicon 0.6v. The BAT41 Paul mentioned should be fine, as would the BAT42 or 1N6263. Note: the STMicroelectronics data sheet has the wrong illustration for the BAT41/42/43 forward voltage drop; it has the curves for an ordinary silicon diode.
Jumpers: Install 3 jumpers at P1 5-6 (RXT to RXD), 47-48 (SO to SI), and 49-50 (VO to VI). These will be removed when you add the expansion board to convert it into a ZX81.
ROM socket: I thought I did include the jumper options to allow both the ZX80 and ZX81 code to be put in the same EPROM. I'll have to look at it again, or test it myself when I get that far. If any changes are needed, I can make them on the next batch of boards.
Germanium diodes have about a 0.25v forward drop. Schottky is around 0.35v, and regular silicon 0.6v. The BAT41 Paul mentioned should be fine, as would the BAT42 or 1N6263. Note: the STMicroelectronics data sheet has the wrong illustration for the BAT41/42/43 forward voltage drop; it has the curves for an ordinary silicon diode.
Jumpers: Install 3 jumpers at P1 5-6 (RXT to RXD), 47-48 (SO to SI), and 49-50 (VO to VI). These will be removed when you add the expansion board to convert it into a ZX81.
ROM socket: I thought I did include the jumper options to allow both the ZX80 and ZX81 code to be put in the same EPROM. I'll have to look at it again, or test it myself when I get that far. If any changes are needed, I can make them on the next batch of boards.
Last edited by Lee Hart on Mon Jul 05, 2010 7:27 pm, edited 1 time in total.
Re: New ZX80 boards
I have both ROMs jumper selectable.
built an image using the following layout:
0..4k ZX80 ROM
4..8k ZX80 ROM (purely for simplicity of creating image)
8..16k ZX81 ROM.
built an image using the following layout:
0..4k ZX80 ROM
4..8k ZX80 ROM (purely for simplicity of creating image)
8..16k ZX81 ROM.
Re: New ZX80 boards
I made a EEPROM with ZX81 + ZX80 + ZX80 ROM inside and tried out a bit.
The printing near w5 doesn't seem to match the schematics.
There is 5V at '27128' where should be A13, and A13 at '2732' where should be 5V. The schematic also states 2716 here, where it should read 2732 like on the board.
This means hat i have to put the jumper to 2732 for using a ZX81 ROM and to 27128 for using a ZX80 ROM.
I also wonder about the ROM and RAM mapping.
IN ZX81-Mode (W4 to ZX81=A12, W5 to 2732=A13)
There must be ROM at adress 0 to 8191, and the ZX80 ROM twice in the area from 8192 to 16386.
The 32K RAM beginns at 16384, but there seems to be another copy of the ROMs in 32768 to 49151.
Then a copy of the 16 K RAM.
So everything above 32K is mirrored. and 16K of ROM and 16K of Rom would be usable in this configuration.
Is there a Reset-resident area of RAM?
I would like to copy programs there as I cannot save to cassette at the moment.
The printing near w5 doesn't seem to match the schematics.
There is 5V at '27128' where should be A13, and A13 at '2732' where should be 5V. The schematic also states 2716 here, where it should read 2732 like on the board.
This means hat i have to put the jumper to 2732 for using a ZX81 ROM and to 27128 for using a ZX80 ROM.
I also wonder about the ROM and RAM mapping.
IN ZX81-Mode (W4 to ZX81=A12, W5 to 2732=A13)
There must be ROM at adress 0 to 8191, and the ZX80 ROM twice in the area from 8192 to 16386.
The 32K RAM beginns at 16384, but there seems to be another copy of the ROMs in 32768 to 49151.
Then a copy of the 16 K RAM.
So everything above 32K is mirrored. and 16K of ROM and 16K of Rom would be usable in this configuration.
Is there a Reset-resident area of RAM?
I would like to copy programs there as I cannot save to cassette at the moment.
In theory, there is no difference between theory and practice. But, in practice, there is.