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 Post subject: Re: LPT EPROM Reader?
PostPosted: Sun Sep 10, 2017 12:40 pm 
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Joined: Sun Apr 13, 2008 11:12 am
Posts: 6442
Location: UK (temporarily)
One thing that immediately pops out to me:

The LM317 has a certain amount of current that flows out of the ADJ pin (50-100µA). Your voltages will be a little bit higher than intended because it wasn't taken into account.

Also, Vin from the parallel port might be 3.3V instead of 5V. You should check, because it'll change the math.

But that's not what you asked.

The page you found does this:
  • bcurrent = IC ÷ hFE
  • baseresistor = (Vinput - VBE) ÷ (3·bcurrent)

He's added a margin of 3 safety factor. Which should account for the difference between the Rb of 430kΩ that you found and the 143kΩ he recommends. I forgot to mention that β is a function of both temperature and the collector current, so derating by a factor of 3 is a reasonable good way to ensure that it'll stay in saturation regardless of the current state of the transistor.

Note that the BC547's Vcesat is probably smaller than the 1.4V you're using. The exact value will change the value of Rc you want to use.


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 Post subject: Re: LPT EPROM Reader?
PostPosted: Sun Sep 10, 2017 1:35 pm 
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Joined: Wed Apr 07, 2010 1:14 am
Posts: 484
Location: Iran
By using the bottom calculator, 120K seems to be a good value for R11 :
Vbe : 0 V
hFE : 110
Ic : 0.001 A
Vi : 3.3 V

By using the above calculator, 100K seems to be a good value for R14 :
Vbe : 0.7 V
Vce : 0.25 V
hFE : 110
RL : 4700
Vcc : 5 V
Vi : 3.3 V


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 Post subject: Re: LPT EPROM Reader?
PostPosted: Mon Sep 11, 2017 12:31 pm 
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Joined: Wed Apr 07, 2010 1:14 am
Posts: 484
Location: Iran
I have tested it for a few times and it seems to work fine.
27C080 Read time : 40 Seconds
27C080 Write + Verify time : 40 + 60 Seconds
OS : Windows XP

When I started this project a few weeks ago, I didn't have any idea on how to make a programmer.
I couldn't be able to do it without lidnariq help, thank you very much.
I have learned a lot from this project.


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EPROM Programmer.zip [324.97 KiB]
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PostPosted: Mon Sep 11, 2017 12:36 pm 
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Joined: Sun Apr 13, 2008 11:12 am
Posts: 6442
Location: UK (temporarily)
You're welcome!


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