4 ms·

That's rather cool. I am slightly obsessed with current loop designs myself. It's amazing that you can deliver sensor power and the data in an analogue or digit

by cjsuk 9y ago

That's rather cool. I am slightly obsessed with current loop designs myself. It's amazing that you can deliver sensor power and the data in an analogue or digital form over two wires over huge distances without degraded performance. Definitely agree with Art of Electronics. Also for some more complicated schematics with rigorous engineering approaches detailed, google for "tektronix 453 manual". It's an analogue learning goldmine!

Animats 9y ago
Constant-current design is rare today, but has its uses. I built this thing because the standard drive circuit for 60mA Teletypes is a 120VDC power supply with a 2K 10W ballast resistor in series. Over 95% of the energy goes into heating up the ballast resistor, and you need a box with ventilation slots to prevent heat buildup. Here's are some U.S. Navy current loop supplies from the 1940s-1950s.[1] There's been progress since then. Powering it entirely from a USB port was done partly for convenience and partly because somebody said it was impossible. The power budget is moderately tight, so it took a moderately advanced power supply design. It draws about 270mA from the USB port. The comment I get from radio hams and Teletype collectors about this is "can you make it in through-hole"? It's all surface mount, because the good parts for modern power supplies are surface mount only. I had to learn how to surface mount solder to do this. So now I have a compressed-air powered solder paste dispenser, a programmed reflow oven, a USB microscope, and some very good tweezers. All solder is lead-free. Once you get the right tools and learn the techniques, surface mount is easier than through-hole. But there's a substantial learning curve. I figured that if I was going to build electronics, I should build the way it's built today, not with 1970s technology. An observation about Silicon Valley: you can't buy many electronic parts in Silicon Valley any more. The stocking distributors are gone. Zacks, Hamilton/Avnet, even Radio Shack are gone. There's still Jameco, but they don't do much surface mount stuff. Have to order from DigiKey or Mouser. Right now, I'm waiting for one surface mount resistor to come in from Minnesota. (One resistor on that board needs to be changed from 16 to 22 ohms.) [1] http://www.virhistory.com/navy/tty-loop.htm http://www.virhistory.com/navy/tty-loop.htm
- cjsuk 9y ago
  Thanks for the detailed reply. Interesting read. I'm a ham as well. I think the through hole stuff is dead. It's difficult and expensive to get a lot of parts now and my huge stockpile is dwindling. I prototype with strips of FR4 sliced up and SOIC/0805 parts now. I'm not going to pay 4x the cost for a TH part! The irony is I still have a 1962 Heathkit VTVM I use regularly with it. The thing is completely immune to RF. Same problem with availability here in the U.K. Our biggest suppliers do free next day delivery though down to single resistors which is pretty good.
  - Animats 9y ago
    (I'm not a ham.)
    - cjsuk 9y ago
      Sorry to be clear I didn't think you were, just sympathising with your point about hams who want everything TH.
- Kliment 9y ago
  I got tired of people telling me they couldn't possibly do surface mount so I developed a two hour workshop and I travel around teaching it. I've had around 470 people do it so far. Apparently the learning curve is compressible, and the equipment can be reduced to a small 15kg travel case :) I use stencils instead of a paste dispenser (more precision and less equipment, and I also show people how to make their own stencils by etching copper film) and a hotplate instead of a reflow oven, and magnifying glasses instead of a USB microscope. It's definitely good enough for prototypes, and the total investment in equipment for someone to assemble their first board is less than $40. I focus on teaching correct technique and taking people's fear of surface mount away.

by cjsuk 9y ago

Animats 9y ago

Constant-current design is rare today, but has its uses. I built this thing because the standard drive circuit for 60mA Teletypes is a 120VDC power supply with a 2K 10W ballast resistor in series. Over 95% of the energy goes into heating up the ballast resistor, and you need a box with ventilation slots to prevent heat buildup. Here's are some U.S. Navy current loop supplies from the 1940s-1950s.[1] There's been progress since then. Powering it entirely from a USB port was done partly for convenience and partly because somebody said it was impossible. The power budget is moderately tight, so it took a moderately advanced power supply design. It draws about 270mA from the USB port. The comment I get from radio hams and Teletype collectors about this is "can you make it in through-hole"? It's all surface mount, because the good parts for modern power supplies are surface mount only. I had to learn how to surface mount solder to do this. So now I have a compressed-air powered solder paste dispenser, a programmed reflow oven, a USB microscope, and some very good tweezers. All solder is lead-free. Once you get the right tools and learn the techniques, surface mount is easier than through-hole. But there's a substantial learning curve. I figured that if I was going to build electronics, I should build the way it's built today, not with 1970s technology. An observation about Silicon Valley: you can't buy many electronic parts in Silicon Valley any more. The stocking distributors are gone. Zacks, Hamilton/Avnet, even Radio Shack are gone. There's still Jameco, but they don't do much surface mount stuff. Have to order from DigiKey or Mouser. Right now, I'm waiting for one surface mount resistor to come in from Minnesota. (One resistor on that board needs to be changed from 16 to 22 ohms.) [1] http://www.virhistory.com/navy/tty-loop.htm http://www.virhistory.com/navy/tty-loop.htm

cjsuk 9y ago
Thanks for the detailed reply. Interesting read. I'm a ham as well. I think the through hole stuff is dead. It's difficult and expensive to get a lot of parts now and my huge stockpile is dwindling. I prototype with strips of FR4 sliced up and SOIC/0805 parts now. I'm not going to pay 4x the cost for a TH part! The irony is I still have a 1962 Heathkit VTVM I use regularly with it. The thing is completely immune to RF. Same problem with availability here in the U.K. Our biggest suppliers do free next day delivery though down to single resistors which is pretty good.
- Animats 9y ago
  (I'm not a ham.)
  - cjsuk 9y ago
    Sorry to be clear I didn't think you were, just sympathising with your point about hams who want everything TH.
Kliment 9y ago
I got tired of people telling me they couldn't possibly do surface mount so I developed a two hour workshop and I travel around teaching it. I've had around 470 people do it so far. Apparently the learning curve is compressible, and the equipment can be reduced to a small 15kg travel case :) I use stencils instead of a paste dispenser (more precision and less equipment, and I also show people how to make their own stencils by etching copper film) and a hotplate instead of a reflow oven, and magnifying glasses instead of a USB microscope. It's definitely good enough for prototypes, and the total investment in equipment for someone to assemble their first board is less than $40. I focus on teaching correct technique and taking people's fear of surface mount away.