Products > Test Equipment
Test Equipment Anonymous (TEA) group therapy thread
m k:
--- Quote from: Vince on March 22, 2023, 09:01:19 pm ---Washing that 7504 did not occur to me.... it's not hollow-state technology, it was not dirty to begin with either, and it was so far gone that restoring it never ever even remotely crossed my mind....
--- End quote ---
My mental image also included a belly up machine handled from the frame with long yellow gloves, a brush resting aside and Bobby Darin rolling on the turntable.
Vince:
You have too much imagination.... I would just use a high-pressure washer at full blast....
Robert763:
--- Quote from: Vince on March 22, 2023, 08:42:15 pm ---No worries, you can't pee in my coffee because I don't drink the stuff, I hate it 8)
You are complicating things... it's not looking simpler to use a "proper" DAC.
As I said I only need a crude DAC, don't care about full scale value or stability, could be +5V or -17V or +27.34V, doesn't matter.
Now I think of it, I remember some gizmo available for sale, that does something similar to what I want to do, and it uses just a SIL ladder connected to the I/O pins of an MCU, nothing else, and it works perfectly...
So I guess I am again guilty of overthinking things...
Hell maybe I will reconsider my position and use an MCU instead of discrete logic chips. Would make the design more compact and easier to modify/fine tune.
I will check the timing requirements of my project and see if an AVR MCU could cope with it or not.
Only reason for discrete logic initially, is to try to fo more with less... it's more satisfying and elegant. But at the end of the day I want this project to come to life, I kinda need it as stepping stone for a larger project, so if an MCU makes more practical sense then I can't rule it out...
I don't want to disclose my project, so I will PM you so you can understand the situation better.... but you will have to sign an NDA first ! :-DD
--- End quote ---
Hi Vince, There are LOTS of simple to use parallel input DAC chips out there. anything from 8 to 12 bits are common. Most don't need any "support" logic, not even a clock. Parallel binary in voltage out. A "multiplying" type will even take a variable voltage in (AC bipolar for many) and multiply the voltage (by a value of 0 to 1) according to the digital input. For example 2V in and 128 (binary for an 8 bit DAC) inputs will give 1V out.
Many many years ago (Blimy nearly 40) I designed an analog gauge for an aircraft that had a complex calibration curve in a ROM. I took 0-10V input. This fed a ADC with free-running clock, Data output connected to the address inputs of the ROM. The data outputs connected to the inputs of a DAC and the output of the DAC drove an analog meter. Not a microprocessor in sight. I didn't even have a PROM progrmmer. It was hand programmed with a bunch of toggle switches. To simplify the PCB layout (hand laid with transfers and tape) to fit it in the case on a single sided PCB I laid the chips side by side and pin to pin. This "scrambled" both the address and data lines Enigma style ???
So I just scrambled the wiring to the switches in the programmer the same way. Years later I was asked to update the calibration because they had changed the airframe. I had to make up a de-scramber adaptor to go between my progammer and the PROM. I've still got it somewhere.
Robert.
German_Engineer:
Yet another 5334B frequency counter OCXO and prescaler retrofit. The OCXO is a rather inexpensive board from aliexpress (TZT store, 2525 OCXO board, BG7TBL, 20USD), since I did not want to spend the money for an original hp part. The board fits nicely and needs only a 7805 to connect to the the always-on 15VDC supply of the counter. I have been watching a 1MHz signal from a GPS receiver for a few weeks now and the OCXO is very stable - only "lots-of-zeros" on the display. Recommended.
Vince:
--- Quote from: Robert763 on March 22, 2023, 10:05:10 pm ---Hi Vince, There are LOTS of simple to use parallel input DAC chips out there. anything from 8 to 12 bits are common. Most don't need any "support" logic, not even a clock. Parallel binary in voltage out. A "multiplying" type will even take a variable voltage in (AC bipolar for many) and multiply the voltage (by a value of 0 to 1) according to the digital input. For example 2V in and 128 (binary for an 8 bit DAC) inputs will give 1V out.
Many many years ago (Blimy nearly 40) I designed an analog gauge for an aircraft that had a complex calibration curve in a ROM. I took 0-10V input. This fed a ADC with free-running clock, Data output connected to the address inputs of the ROM. The data outputs connected to the inputs of a DAC and the output of the DAC drove an analog meter. Not a microprocessor in sight. I didn't even have a PROM progrmmer. It was hand programmed with a bunch of toggle switches. To simplify the PCB layout (hand laid with transfers and tape) to fit it in the case on a single sided PCB I laid the chips side by side and pin to pin. This "scrambled" both the address and data lines Enigma style ???
So I just scrambled the wiring to the switches in the programmer the same way. Years later I was asked to update the calibration because they had changed the airframe. I had to make up a de-scramber adaptor to go between my progammer and the PROM. I've still got it somewhere.
Robert.
--- End quote ---
Thanks for the story, I always love them ! :-+
Good news on the DAC front then... do you have suggestion of brands and models / series that are easily available these days ?
I guess I will want a couple 9 or 10 bit ones.
Problem is that the parametric search on Mouser probably does not allow to filter for "CPU-less" DAC sadly.
So unless I know what models to look for, I could spend my life checking thousands of datasheet one by one....
However as you said, at the least, a multiplier DAC would fit my needs, and maybe it's not unreasonable to expect the parametric search to have a "multiplier" keyword somewhere.... let's see...
Then sort by price, package type, stock/availability....
You were brave programming that EPROM by hand with switches... hopefully it was not a 27C4000....
You were young and motivated I guess >:D
Sounds like the kids back then who programmed their Altair computer the same way.... sure takes some love....
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