Jump to content
spookt

USB PSU

Recommended Posts

HI Folks

 

Since I have exactly one original UK PSU (which I'm getting a little concerned about) I decided to look into alternatives. Given that I'm (always) on a budget I thought I'd look at USB power since I have a large number of adapters / chargers lying around and USB is a standard so getting replacements should be plug and play, right? I made up a couple of cables, wiring USB Vcc and GND to a 5 pin DIN and connecting the three pins on each side together so three pins are tied to Vcc and three to GND. Checked the polarity and finally tested on an 8 bit.

 

All seemed fine, the machine booted and seemed to function well, until I tried IO and in particular my SIDE cart. Running from USB power the machine refused to recognise the CF media, showing "no media". I guessed this might be a lack of power so ordered up a couple of beefier USB adapters (decent brands not cheap Chinese crap), one a 2.4A until and one 3A. When they arrived I got exactly the same behaviour. SIO to SIO2PC or straight to floppy has issues too.

 

I decided to measure the volts coming into the machine from the rear of the power jack, and found that all of the USB supplies I have on hand sit at about 5.2V until the machine is powered on and then all immediately drop to about 4.3V once under load. The original legacy PSU sits at about 5.2V once the machine is running. So a lack off volts would appear to be the issue.

 

My question is that I've seen / read / heard accounts of other folk using USB power and so if you are, what are you using as a PSU and have you noticed any issues with instability or malfunction using a USB supply? 

 

 

Share this post


Link to post
Share on other sites

That's interesting.

I went down the splicing a new PSU to the old din plug route and have no issues with powering sdrive_micro or xc12 

Share this post


Link to post
Share on other sites
33 minutes ago, spookt said:

5 pin DIN

i think it should be a 7-pin DIN - check the socket

Share this post


Link to post
Share on other sites

I did this, it's a prototype for a custom PCB that I never bothered to continue with, now I use spare Raspberry Pi power supplies, I've had no issues at all. I thought there was one with Fujinet but it turned out to be a timing issue.

 

IMG_2786.thumb.jpeg.ab56bfcc2aab6f5da5dc581286270468.jpeg


IMG_2793.thumb.jpeg.5f6d8241c53c6eb740df798017022a32.jpeg


 

  • Like 3

Share this post


Link to post
Share on other sites

I was just thinking about a USB PSU this morning so I am looking to see the replies, I have 2 PSU's but one is an ingot so I really only have one PSU that is safe to use.

 

I'd also be keen to hear about anyone with a USB PSU and an AVG cart and possibly a sys checker combination if it all works..

Share this post


Link to post
Share on other sites

I used a 130XE powered by a USB PSU (2A) with a Sophia inside for many years now with cartridges like MyIDE II, SIDE2, etc.

I also use the excellent SYS-CHECK from time to time without any problem.

I have been using it recently as a memory extension with no issue at all with the above cartridges.

So no worries as soon as it has enough power.

I won't come back to the brick...

Share this post


Link to post
Share on other sites

FYI - the power block for the USB should only be 1.5 amp for a stock system a  2.0 amp if you have an ultimate 1mb and other things added to your system. Not sure if that would make a difference or not, but worth mentioning. If this is a 1200xl, you have to remove a resistor ( put a wire in its place ) to restore +5 volts to the SIO port.

Edited by Paul Westphal

Share this post


Link to post
Share on other sites
53 minutes ago, xrbrevin said:

i think it should be a 7-pin DIN - check the socket

Apologies - typo. It is indeed 7 pins. 3 tied to Vcc, 3 to ground and 1 unused. 
 

Interesting that others are having no issues with this kind of thing but I’ve tried several USB supplies of varying manufacture and rating and have the same results with all of them, yet the system is rock solid with the original PSU. 

Share this post


Link to post
Share on other sites
16 minutes ago, Paul Westphal said:

FYI - the power block for the USB should only be 1.5 amp for a stock system a  2.0 amp if you have an ultimate 1mb and other things added to your system. Not sure if that would make a difference or not, but worth mentioning. If this is a 1200xl, you have to remove a resistor ( put a wire in its place ) to restore +5 volts to the SIO port.

Thanks Paul. It’s a 600XL so no lack of SIO power. My understanding on the amps rating of a PSU is that it’s the max supply so should only matter if it’s under rated rather than over rated. The PSU won’t supply ‘too many amps’ in other words. 

Share this post


Link to post
Share on other sites

Overrated power supplies are only an issue with regard to efficiency. If you put an 800W PS in your PC that only draws 125W, it won't be very efficient. Better use ~200W PS. But that's just a small difference on your electricity bill. Nothing else.

 

  • Like 1

Share this post


Link to post
Share on other sites

Looks like there's some other weirdness going on here so I need some time to sit down and do some proper testing. The machine will boot into SDX from the U1Mb and reads the CF card fine. It passes IDEDIAG with no issues, but now reports no media in the loader whether I use the stock PSU or the USB supply. I've tested with two different CF cards, one pulled straight from the Incognito in my 800 which works fine there.

 

We're about to head out to see friends for diner so I'll have to play more tomorrow. Thanks for all the feedback so far.

Share this post


Link to post
Share on other sites

My USB PSU - 2A  works fine, no issues with external devices either.

 

I also have a multi-USB adapter and I plug the other XL through the 2a socket on that too. Again no device issues with this either.

Share this post


Link to post
Share on other sites

The power supply should maintain the rated voltage when drawing the maximum rated current, so if it's dropping to 4.3V either the supply is faulty or mis-advertised or your system is drawing more current than it should...

Share this post


Link to post
Share on other sites

A compliant USB source will only provide 500mA (USB 1.0 or USB 2.0) or 900mA (USB 3.0) until you negotiate with the provider chip for more power.  Some are not compliant and will deliver their full load without negotiation.  In this case, such noncompliance is a useful trait.  Otherwise you need a chip on the power input that will ask for higher amperage (maybe even voltage) to get what you require.

 

The problem with under-volting is that it can damage some electronics.  Many digital chips are made to operate in either full on or full off, so the power requirements of the switch are small.  When you go into an under-volt situation, its transistors can be forced to operate in the linear zone, and that causes the power handling requirements to rise dramatically.  If the transistor wasn't designed for the required power, it overheats and dies.

 

Many modern electronics are made to cope with that, and in fact electronics in safety-critical systems are required to survive under-volt situations without damage.  But vintage electronics may not be so well-designed, so beware.  4.3V is definitely lower than the TTL requirements.

 

  • Like 1

Share this post


Link to post
Share on other sites
21 hours ago, Mr Robot said:

I did this, it's a prototype for a custom PCB that I never bothered to continue with, now I use spare Raspberry Pi power supplies, I've had no issues at all. I thought there was one with Fujinet but it turned out to be a timing issue.

You can't go wrong using Raspberry Pi USB PSU's, it's what they are made for, the one for the Pi 3B/3B+ is 2.5A which is fine for our 8 Bits, if you want a 

bit more in reserve  the Pi 4 PSU is 3A

Share this post


Link to post
Share on other sites

Thanks for the breakout board idea.

 

I've ordered 2 - should have got more - I have a lantern which charges by micro-USB and the port just sheared off the board.  I was just going to replace it with a barrel connector but now I think I'll use one of these guys instead and relocate it somewhere where hopefully it'll be more solidly mounted.

And of course the other to use for the Atari.

Share this post


Link to post
Share on other sites

Just one more thing to keep in mind when deciding on using a non-Atari PSU for your 8-Bit.

 

Atari 5V PSU (600XL-130XE) uses a linear regulator IC generically called a 7805 to regulate and hold the voltage at 5 VDC. These tend to produce a very uniform voltage level independent of when they are cold (just plugged in) or hot (having been run for several hours or days). So in other words they have very good stability and consistency as to what the actual voltage is that is coming out.

 

USB and similar PSU uses switching regulation technology with feedback to regulate and hold the voltage at 5 VDC. Depending upon the circuit used to perform this function, it can either be as stable as a linear regulator, or considerably worse (more likely). The problem is you don't know what you'll get unless you've specifically had past experience with a given brand (even that could change). Usually the voltage variance is not enough to cause issues with a device working, or to cause damage to it. However due to the way the Atari 8-Bit adjusts its color, using a voltage doubler in a voltage divider circuit with a potentiometer feeding the GTIA color adjust pin, even a 'slight' variance in voltage can cause a very noticeable color shift. So in other words you might find that color is never the same between uses, or in other cases requires an extended run time before it settles down and locks in. This can even happen with the linear regulated supplies, but tends to last for only seconds instead of minutes.

 

I saw the color shift problems on the 1088XEL which was based on a using switching PSU technology. It would take many minutes of operation before the color would settle. When I went on to develop the 1088XLD I decided to cure this problem once and for all, by using a precision 10V zener diode to down regulate the XLD's 12 VDC supply to supply a constant voltage independent of time or temperature changes to be used for the voltage divider color adjust pot. This did the trick, and gives the XLD very stable color phase under all conditions, only requiring a one time adjust (set it and forget it). And it pretty much runs with the correct color right from the get go after being powered on for the first time. Obviously this approach won't work for the XL/XE situation, but it does point to the importance of using a very stable voltage PSU with those systems.

 

  • Like 5

Share this post


Link to post
Share on other sites

I used a genuine Raspberry Pi PSU, and when my 130XE was using a SD2SIO, I had interference on screen.  Thinking this was inadequate filtering in the PSU and 130XE, added a small box, with a few capacitors across the power rails, between the Atari and PSU.  It worked perfectly.  

 

Since then the XE has had a U1MB, dual Pokey, UAV, and a SDrive Max added, and the Pi PSU with additional filter caps still works perfectly.

 

Wish I had a spare Cisco 5V 3.0A PSU to hack a DIN plug on, suspect its got enough filtering onboard to work with the XE.

Share this post


Link to post
Share on other sites

At the Maarssen gatherings, we regularly use an IKEA KOPPLA that has built-in USB ports and they work marvelously.

 

Share this post


Link to post
Share on other sites

I use a USB PSU with my 800XL. It’s just an Atari DIN to USB cable that I bought from eBay. I’ve tested it with Samsung 2A, Apple 1A and plugged direct into a USB3 port on a PC with no problems using a Lotharek SIO2SD device. 

Share this post


Link to post
Share on other sites
2 hours ago, marauder666 said:

I used a genuine Raspberry Pi PSU, and when my 130XE was using a SD2SIO, I had interference on screen.  Thinking this was inadequate filtering in the PSU and 130XE, added a small box, with a few capacitors across the power rails, between the Atari and PSU.  It worked perfectly.  

 

Since then the XE has had a U1MB, dual Pokey, UAV, and a SDrive Max added, and the Pi PSU with additional filter caps still works perfectly.

 

Wish I had a spare Cisco 5V 3.0A PSU to hack a DIN plug on, suspect its got enough filtering onboard to work with the XE.

Which Cisco PSU are you referring to ? I have a lot of Cisco gear so might be an interesting option.

Share this post


Link to post
Share on other sites

Another thought is about the cable you used. I know some usb cables can't support fast charging because they only use one conductor. I'd be interested to know of there's a voltage drop across your cable. 

 

Share this post


Link to post
Share on other sites
6 hours ago, mytek said:

... this approach won't work for the XL/XE situation...

 

Could the Zener not be added to an XL?

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...

  • Recently Browsing   0 members

    No registered users viewing this page.

×
×
  • Create New...