Embarking on an Altair 8800C build

Discuss construction, troubleshooting, and operation of the Altair 8800c computer

Re: Embarking on an Altair 8800C build

Postby BillO » August 2nd, 2022, 3:39 pm

Also, the LEDs today are many times brighter than they were in the 70s. Unless you want to light up a room with them you might want test them first and choose your resistors for reasonable light output.
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Re: Embarking on an Altair 8800C build

Postby TheoAU » August 3rd, 2022, 4:56 am

Wayne Parham wrote:I'm not sure the forward voltage is all that relevant. I even have blue LEDs in one of my builds - which require much higher forward voltage - and they look great. I think more an issue is the lumens per mA and the diffusion. And one more important factor: the lead length. Some LEDs have long leads but some barely make it.

All that said, in my opinion, the "good old" generic T1-3/4 (5mm) LEDs we were all familiar with in the 1970s are what you want. They are diffused and have a color and brightness that work well in the Altair. You definitely don't want a non-diffused LED but other than that, most of 'em will work.


I saw the pictures of your blue LED version, it looks great. I got a sample LED for my local Jaycar store today and I'm not happy with how it looks. Even without powering it up, it looks cheap and the red lens is very light. The HLMPD150A and the HLMP-D101 have a nice dark premium look to them similar to the ones on the original Altair. I'll go with the HLMP-D101 they are available at both Digikey and Mouser.

Wayne - what resistors did you use with the HLMP-D101 LEDs?
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Re: Embarking on an Altair 8800C build

Postby TheoAU » August 3rd, 2022, 4:57 am

BillO wrote:Also, the LEDs today are many times brighter than they were in the 70s. Unless you want to light up a room with them you might want test them first and choose your resistors for reasonable light output.


Thanks BillO. Yes, I'll go with the HLMP-D101 and the resistors recommended for those.
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Re: Embarking on an Altair 8800C build

Postby AltairClone » August 3rd, 2022, 9:38 am

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Re: Embarking on an Altair 8800C build

Postby TheoAU » August 3rd, 2022, 7:58 pm

AltairClone wrote:Mouser has over 500 in stock: https://www.mouser.com/ProductDetail/Br ... QPkg%3D%3D

Mike


Hi Mike,

When I view that page, it says zero stock for me. It must change based on where you're located. Good news is, I've found a supply of HLMP-D150 at Element 14. So I'll get them from there.
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Re: Embarking on an Altair 8800C build

Postby Wayne Parham » August 4th, 2022, 8:36 am

TheoAU wrote:Wayne - what resistors did you use with the HLMP-D101 LEDs?

I used the 2KΩ resistors Mike calls for in his schematic and BOM. I used that value for both my "red" and "blue" builds. They both have what I would consider to be the "proper intensity" and they look great.

As an aside, I find that LEDs illuminate pretty brightly with very low current. Light perception must be like sound perception, on a logarithmic scale.

For example, I have a little audio preamp controller that I developed for tube amp manufacturers. It controls RDACs to provide remote-controlled volume and balance. And it also includes an input switcher to control what source is active. The audio controller is based on an Atmel AT2313 (or AT4313), which monitors (front panel) push-button inputs and senses pulses from an IR receiver that reads the remote. It is also connected to the RDACs and to a bunch of LEDs that show power (on/off), input selected and volume.

I initially chose LED current-limiting resistors, the "normal" way, calculating the value based on voltage across the resistor and the desired current, basically 10mA or 20mA. Kinda standard. Works great for giving a nice safe resistor value that turns the LEDs on all the way without smoking them.

But man, the LEDs I chose for the prototype would put your eyes out. And they're not even the super bright LEDs that need heatsinks. They're just little-bitty things. But they'll still put your eye out.

So I started dialing back the current with higher and higher resistance levels. Ended up with a crazy high resistance of 12KΩ, and even that seems too bright.

All that to say the days of running a 220Ω or 330Ω series resistor to an LED with a 5v source are gone for me. They're
just too dang bright!
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Re: Embarking on an Altair 8800C build

Postby TheoAU » August 14th, 2022, 4:03 am

Wayne Parham wrote:
TheoAU wrote:Wayne - what resistors did you use with the HLMP-D101 LEDs?

I used the 2KΩ resistors Mike calls for in his schematic and BOM. I used that value for both my "red" and "blue" builds. They both have what I would consider to be the "proper intensity" and they look great.

As an aside, I find that LEDs illuminate pretty brightly with very low current. Light perception must be like sound perception, on a logarithmic scale.

For example, I have a little audio preamp controller that I developed for tube amp manufacturers. It controls RDACs to provide remote-controlled volume and balance. And it also includes an input switcher to control what source is active. The audio controller is based on an Atmel AT2313 (or AT4313), which monitors (front panel) push-button inputs and senses pulses from an IR receiver that reads the remote. It is also connected to the RDACs and to a bunch of LEDs that show power (on/off), input selected and volume.

I initially chose LED current-limiting resistors, the "normal" way, calculating the value based on voltage across the resistor and the desired current, basically 10mA or 20mA. Kinda standard. Works great for giving a nice safe resistor value that turns the LEDs on all the way without smoking them.

But man, the LEDs I chose for the prototype would put your eyes out. And they're not even the super bright LEDs that need heatsinks. They're just little-bitty things. But they'll still put your eye out.

So I started dialing back the current with higher and higher resistance levels. Ended up with a crazy high resistance of 12KΩ, and even that seems too bright.

All that to say the days of running a 220Ω or 330Ω series resistor to an LED with a 5v source are gone for me. They're
just too dang bright!


Due to the need for more energy efficiency in lighting in recent years, there's been a great deal of effort put into improving the brightness of LED's. You see it SUV headlights, they're blinding as they pass you at night.
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Re: Embarking on an Altair 8800C build

Postby TheoAU » August 14th, 2022, 4:24 am

The only parts I'm still waiting to arrive are the case and front panel boards, and they're on the way. While waiting, I put together the nine slot backplane and power supply wiring. Everything tests well, I've got the correct voltages going to the correct pins. I'm getting 7.61v, 15.12v and -15.12 on respective pins.

LED's arrived they look great. They have a deep red look, I held them up to the original machine and they're a perfect match.

Here are some updated pics.
Attachments
20220814_160901.jpg
20220814_160729.jpg
20220814_160701.jpg
Last edited by TheoAU on August 14th, 2022, 6:35 pm, edited 1 time in total.
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Re: Embarking on an Altair 8800C build

Postby AltairClone » August 14th, 2022, 7:25 am

Waiting is the hardest part!
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Re: Embarking on an Altair 8800C build

Postby TheoAU » August 17th, 2022, 10:29 pm

Case and front panel boards arrived yesterday. The Clone case is great. The design is simple and light compared to the original, but very well thought out. A really good match in looks with the original.

It's full steam ahead with the build. I have all the parts now. The motherboard, power supplies and CPU are done. I just need to put the front panel components together!
Attachments
20220818_075436.jpg
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