Threaded Mode | Linear Mode

Harald · 05-05-2019, 11:55 AM

(05-05-2019 11:04 AM)Robert VM Wrote: I may have misunderstood...
Aren't the different voltages meant to keep junctions (or FET equivalents) (reverse) polarised.
Operating from the same supply may get the device into all conducting and overheating?
Robert

I am not sure but I also would expect the two voltages are needed. What I meant is that they probably just don't need to be tightly regulated. So I would try the voltage doubler and a voltage regulator (or possibly just a voltage drop across diodes) to generate the lower voltage from the higher.

teenix · (This post was last modified: 05-05-2019 12:13 PM by teenix.)

(05-05-2019 11:04 AM)Robert VM Wrote: I may have misunderstood...
Aren't the different voltages meant to keep junctions (or FET equivalents) (reverse) polarised.
Operating from the same supply may get the device into all conducting and overheating?
Robert

There aren't any original logic chips remaining in the new CPU board. The card reader runs on GND and 6V only, plus Vbatt to run the motor. The cathode driver is Vbatt and GND and the display anode driver has just GND and a current source to keep the LEDs lit properly with variations in battery voltage.

I think these are all probably bipolar chip types. The card reader might be different as it may have to connect via internal CRC logic down to the -12V rail - not sure as there are no details. Either way, there is no PMOS logic that I am aware of.

I'm just guessing about the 5.5V. The 6 volt to the card reader may be there just because of the available 6 volt rail for the PMOS, so it might be happy with 0.5V less to operate on. I'm not sure I want to experiment on how high the voltage can go with an unregulated supply.

cheers

Tony

Harald · 05-05-2019, 12:21 PM

Oh, I see. I thought the card reader also required both voltages.

Robert VM · 05-05-2019, 10:22 PM

Thanks for explaining, Tony.
Robert

teenix · (This post was last modified: 05-06-2019 12:12 AM by teenix.)

(05-05-2019 10:22 PM)Robert VM Wrote: Thanks for explaining, Tony.
Robert

No problem Smile

It is quite an ingenious setup, having the battery power all the heavy current items directly. That way only a small power supply is all that's needed for the logic. That was why there has been effort put into regulating the LED, motor and print head currents because of the ever changing battery conditions.

cheers

Tony

teenix · 05-06-2019, 09:31 AM

Hi all,

It seems the card reader does require the 6V rail. It reads but won't write at 5.5V

cheers

Tony

teenix · (This post was last modified: 05-07-2019 09:55 AM by teenix.)

(05-05-2019 09:36 AM)Harald Wrote: Thanks for the schematic and layout. You have kept the Cathode of D3 close to C8, that is good. But the track from U7 pin 1, which is the internal switch, to D3 is quite long. You would want to keep that as short as possible to minimize inductance in that path. You are better of moving the choke a bit further away and moveing the diode closer.
It is important to place diode and input and output capacitor close to the IC. You need to minimize path length in all the paths that carry switched currents. The inductor path is not critical.

Hi Harald,

I have squeezed all the relevant parts as close as I can to the IC and given it as much ground plane as I can. Hopefully better.

However, it might be a moot point now. I can't fathom why I was not doing an inductorless design. I had it in my mind that I was looking at reasonably high currents but that is not the case. The new CPU board only draws a few milliamps as does the reader chip, so I think I will scrap the inductor. I've ordered some oscon caps and an LM2665M6 which is similar to Maxim but way cheaper just to try out.

cheers

Tony

cheers

Tony

Harald · 05-07-2019, 12:26 PM

(05-07-2019 01:49 AM)teenix Wrote:
(05-05-2019 09:36 AM)Harald Wrote: Thanks for the schematic and layout. You have kept the Cathode of D3 close to C8, that is good. But the track from U7 pin 1, which is the internal switch, to D3 is quite long. You would want to keep that as short as possible to minimize inductance in that path. You are better of moving the choke a bit further away and moveing the diode closer.
It is important to place diode and input and output capacitor close to the IC. You need to minimize path length in all the paths that carry switched currents. The inductor path is not critical.

Hi Harald,

I have squeezed all the relevant parts as close as I can to the IC and given it as much ground plane as I can. Hopefully better.

However, it might be a moot point now. I can't fathom why I was not doing an inductorless design. I had it in my mind that I was looking at reasonably high currents but that is not the case. The new CPU board only draws a few milliamps as does the reader chip, so I think I will scrap the inductor. I've ordered some oscon caps and an LM2665M6 which is similar to Maxim but way cheaper just to try out.

cheers

Tony

cheers

Tony

Hi Tony,

Yes, that does look a lot better now! Still, if you can do the charge pump, that would be the better solution in my opinion.

Cheers,
Harald

teenix · 05-09-2019, 01:27 AM

Hi all,

Last test completed.

The write protect override option worked ok. The new CPU can re-write a write protected card if this option is set. The reader will operate normally if this option is clear. It can be set/cleared using the new menu system or from the PC.

New PCBs in for manufacture - fingers crossed :-)

cheers

Tony

teenix · (This post was last modified: 07-17-2019 01:56 AM by teenix.)

Hi all,

Still poking away at the new CPU boards.

I had to sell my house because it was sinking into an easement, so staying at dear old mums until I find something new.

This is my illustrious work bench. No room to swing a cat, but managing to keep going :-)

I put together a small PC program to format and send data to a controller so I can more easily test the Classic display just be typing it and it appears. Harald's test LED idea (thanks) is not lighting so things are looking good.

Still waiting on new PCB's for HP-67 CPU board.

cheers

Tony

Paul Dale · 07-17-2019, 06:52 AM

If you are willing to travel circa 2Mm north, I could possibly find an alternate place to stay. At least for a while. At least it is warm up here Smile

For those not in the know, Tony lives in the same country as I do but is roughly the distance from Athens to London away from me.

Pauli

teenix · (This post was last modified: 07-18-2019 12:18 AM by teenix.)

(07-17-2019 06:52 AM)Paul Dale Wrote: If you are willing to travel circa 2Mm north, I could possibly find an alternate place to stay. At least for a while. At least it is warm up here

For those not in the know, Tony lives in the same country as I do but is roughly the distance from Athens to London away from me.

Pauli

A cool offer? :-)

I thought about retiring up there in the warmth, but my daughter won't be happy. Too far away.

I've tested the Classic display for different digits and bleed issues. So far it all seems good.

cheers

Tony

**rprosperi** · 07-18-2019, 02:14 AM

(07-17-2019 06:52 AM)Paul Dale Wrote: If you are willing to travel circa 2Mm north, I could possibly find an alternate place to stay. At least for a while. At least it is warm up here

Going North to get warm?!? You guys must live in an upside down part of the world... Smile

teenix · 07-18-2019, 02:29 AM

(07-18-2019 02:14 AM)rprosperi Wrote: Going North to get warm?!? You guys must live in an upside down part of the world...

One of us is living on the [1/X] key :-)

cheers

Tony

teenix · 07-18-2019, 02:31 AM

Hi all,

The HP-67 CPU boards just arrived :-)

They fit ok, so now to populating and fingers crossed...

cheers

Tony

Harald · 07-20-2019, 07:29 PM

(07-18-2019 02:31 AM)teenix Wrote: Hi all,

The HP-67 CPU boards just arrived :-)

They fit ok, so now to populating and fingers crossed...

cheers

Tony

Looks good! Fingers crossed there are no big issues with it!

I'll order at least one when they are available.

teenix · (This post was last modified: 07-21-2019 03:41 AM by teenix.)

(07-20-2019 07:29 PM)Harald Wrote: Looks good! Fingers crossed there are no big issues with it!

Adding to the uphill battle, sadly there is :-(

As hard as I tried, even with flux paste, about a third of the PCB pads for the IC's will not take to the solder with the chips in place. This has never happened before so not sure why. Also some of the chips I ordered had wider pin spacing to the ones in the data sheet. I think I can just get can get away with this, but as they are so small, it's a fiddly fix.

Very frustrating so had to take a break. All I can think to do is clean the pads thoroughly and try wetting them with solder before placing the chips.

I also played with the Classic anode driver timing by shifting the point where the 5 data lines are written by about 1uS and the display seems fine. Due to the PIC's internal hardware, it takes 3-5 instructions to sense the clock reference. Then 3 more to recall and output the data to the anode driver (total average 875nS). I triggered on the falling edge of PHI_1 and that caused it to stop working, so a bit too early. However, this timing delay works ok after the falling edge of PHI_2 which is quite late. I settled on the rising edge of PHI_1 and the data is output just after the falling edge of PHI_2 which is somewhere in between. Not quite exact and a tiny bit of jitter, but it seems happy.

cheers

Tony

mfleming · 07-21-2019, 02:29 PM

(07-21-2019 03:13 AM)teenix Wrote: Very frustrating so had to take a break. All I can think to do is clean the pads thoroughly and try wetting them with solder before placing the chips.

Give it a scrub with a microfiber cloth soaked in 90% IPA. The PCB process can leave behind some contamiate they don't always bother to clean up. Definitely improves my success rate.

Harald · 07-22-2019, 09:37 AM

(07-21-2019 03:13 AM)teenix Wrote:
(07-20-2019 07:29 PM)Harald Wrote: Looks good! Fingers crossed there are no big issues with it!

Adding to the uphill battle, sadly there is :-(

As hard as I tried, even with flux paste, about a third of the PCB pads for the IC's will not take to the solder with the chips in place. This has never happened before so not sure why. Also some of the chips I ordered had wider pin spacing to the ones in the data sheet. I think I can just get can get away with this, but as they are so small, it's a fiddly fix.

Very frustrating so had to take a break. All I can think to do is clean the pads thoroughly and try wetting them with solder before placing the chips.

I also played with the Classic anode driver timing by shifting the point where the 5 data lines are written by about 1uS and the display seems fine. Due to the PIC's internal hardware, it takes 3-5 instructions to sense the clock reference. Then 3 more to recall and output the data to the anode driver (total average 875nS). I triggered on the falling edge of PHI_1 and that caused it to stop working, so a bit too early. However, this timing delay works ok after the falling edge of PHI_2 which is quite late. I settled on the rising edge of PHI_1 and the data is output just after the falling edge of PHI_2 which is somewhere in between. Not quite exact and a tiny bit of jitter, but it seems happy.

cheers

Tony

Hi Tony,

If you like you can send a kit (I'll pay for it) and I can try assembling. My address has changed and I am not sure if you have the new one already, so please make sure before sending anything...
I had to play with the timing on the display driver as well. I can't remember what I settled on (I could look it up if you like). But the display did not work initially when I triggered the DMA on the clock edge I expected to be correct.

Cheers,
Harald

teenix · (This post was last modified: 07-25-2019 07:38 AM by teenix.)

(07-21-2019 02:29 PM)mfleming Wrote: Give it a scrub with a microfiber cloth soaked in 90% IPA. The PCB process can leave behind some contamiate they don't always bother to clean up. Definitely improves my success rate.

I gave a new board a good scrub and seemed better, thanks :-)

(07-22-2019 09:37 AM)Harald Wrote: Hi Tony,

If you like you can send a kit (I'll pay for it) and I can try assembling. My address has changed and I am not sure if you have the new one already, so please make sure before sending anything...
I had to play with the timing on the display driver as well. I can't remember what I settled on (I could look it up if you like). But the display did not work initially when I triggered the DMA on the clock edge I expected to be correct.

Cheers,
Harald

Hi Harald,

Sorry for delay.

As I am definitely not an electronic engineer, I think I might have bitten off a bit more than I can chew. It "seemed" to work fine with the through hole processors, but now it just won't fire up properly at all. I can get 0.00 on the HP-67 display "sometimes" but it is not reliable any more for reasons that escape me. The software simulates ok, and ran ok previously, but not in this hardware.

It might be poor power supply design, but otherwise I've run out of ideas. Below is a CRO snap shot at power up on the 8V rail which propagates through the other supplies. With a 5V scale, it's showing a 12V negative spike which might initially upset the PICs, not sure. After settling down, the supply rails have very low ripple.

Unfortunately, I'm not really geared up for surface mount development, and it is proving to be costly and time consuming, so not sure if I can continue.

cheers

Tony

Edit: Hmmm, I couldn't resist and had to play some more. I tapped into the code on both processors, and just have a blinking LED working from each. Both perform as I expected after multiple quick or slow power on/off cycles. This would seem to suggest that they are happy working in their surroundings, so it appears maybe some bug has crawled into the code on either or both of them. If so, tracking down a fault with two interacting processors will be a tad difficult.