Powering Arduino Mini from GPIB???? - Page 1
Forum section: electronics / beginners

author: GumpyGus
author_rank: Newbie
timestamp: June 23, 2022, 03:10:27 pm
content: I get lots of ideas.I want to network my computers with about a dozen pieces of test equipment through their old but honorable HPIB/GPIB interfaces.But I HATE all those thick and expensive GPIB cables. With a passion of a thousand burning suns (I know, it's not burning, per se )Here's the idea:Hang an Arduino with a Bluetooth interface onto each GPIB port. A little code, and we just might have the ability to communicate with a computer. Never mind having instruments all see the data, that's probably not ever needed. So basically, test EQ to computer and back.Now an Arduino draws like 20 milliamps. I don't want to have to have batteries at each Arduino, and wired power is still a bit mess soooooo:How about borrowing power from the like 20 GPIB data lines?As a rough guesstimate, if we put diodes pointing to a common power bus, anodes to the 20 or so GPIB data lines, and we borrow, say 1 milliamp from each one, the voltage should not droop tooooo much, not enough anyway to look like a logic zero. So we have 20 milliamps at some voltage, with schottky diodes, maybe 3 volts? So if we have powered down the Arduino CPU and BlueeTooth chip, with a CPU wakeup from the GPIB strobe line, and hang say a 220,000uF capacitor to all the diode cathodes, will that work? The duty cycle with the Arduino woken up should be pretty low, maybe as low as 10%. So the somewhat optimistic numbers are 10% duty cycle, say 20 milliamps for 10% of the time, 2 milliamps average, spread over 20 pins, so 100 microamps average drain, that just might be little enough to not kibosh the GPIB strobe lines? Or if that pulls the strobe lines too low, just load down the ?15? or so non-strobing lines?If we have to, we could boost up the voltage with one of those 99 cent Chinese boost regulators with the wonderful-looking 1549 boost IC.Any ideas if we are anywhere close to viability? Am I totally nuts?Regards,GeorgeAG0I

author: GumpyGus
author_rank: Newbie
timestamp: June 23, 2022, 03:27:28 pm
content: oops, update: there are 8 data lines and roughly 8 strobed lines, so at best 16 lines that might be able to supply a little power.And if we need to wake up the Arduino CPU if any strobe line goes low, that's going to require an 8-input NOR gate or 8 diodes. Minor little detail!Oh wait, on the studlier CPUs any input pin can be configured as an interrupt wake-up, so no need for a 8-input NAND. Never mind.So we are up to 20/16 or around 125 microamps average per line. Doable? I'm going to try it as soon as my bag of 50 Chinese 1N60P diodes arrives, in 30 days or so. Dang Radio Shack, why did you have to close down?

author: macboy
author_rank: Super Contributor
timestamp: June 23, 2022, 07:14:05 pm
content: Old school HPIB/GPIB devices have open-collector data lines and handshake lines (5 of them IIRC). Each of these has Thevenin termination of a 3.1k resistor to +5 V and a 6.2k resistor to GND, so the lines idle at about +3.3 V (perfectly legal TTL High level, since > 2.0 V). So with 13 lines, you have effectively about 258 Ohms pulled up to +3.3 V. You should have no issue drawing just a couple mA average from this through some diodes, but the diode drop will result in less than 3 V unless you use some very low forward voltage Schottky diodes (Hint: lower reverse blocking voltage spec usually means lower forward voltage for Schottky diodes). So maybe if you run a 8 MHz device, or use a lower power boost converter it might work.High speed GPIB devices may drive the data lines high and low when talking, and put them into a high impedance state when listening. This means that when your Arduino device is talking (sending a command) it needs to drive the lines high. The handshake lines are still always open-collector. This might be less likely to succeed, as you can only depend on the handshake lines to provide power, and you need more power to drive the data lines high.

author: AndyBeez
author_rank: Frequent Contributor
timestamp: June 23, 2022, 08:30:48 pm
content: Do you have a schematic for your concept?I asume you're using the IEEE488 bus standard to charge a super cap? Your 'arduino' is a what? A mini is just an ATmega328 and a serial chip. To keep power consumption low with Bluetooth, you'll need instead an ESP32 based device or similar.

author: maxwell3e10
author_rank: Frequent Contributor
timestamp: June 23, 2022, 09:40:12 pm
content: I actually tried something along these lines:https://www.eevblog.com/forum/projects/ar488-arduino-based-gpib-adapter/msg3417104/#msg3417104The challenge is that standard HC-05 Bluetooth takes too much current and BLE is hard to use with serial communication. I got a few other low power bluetooth modules and plan to play with them sometime to get lower current consumption.

author: wizard69
author_rank: Super Contributor
timestamp: June 24, 2022, 02:17:05 am
content: Quote from: GumpyGus on June 23, 2022, 03:10:27 pmSo do I and that is when the trouble starts.QuoteYou should hate those cables, far too much bulk for a modern solution.QuoteI don't like that idea.QuoteHere is a suggestion that might be a better long term solution using modern hardware. Consider setting up a Power over Ethernet solution and use that standard to power each of your interface cards. Granted this implies buying a POE switch and a bit more complexity on your interface cards but you will likely have 30 watts available to run that Arduino. Beyond that if you want to interface to things with ports other than GPIB, you will have a good portion of the hardware already done. You might want to chose a slightly different Arduino compatible processor that easily supports Ethernet but over all, you will or should be able to create a "generic" Ethernet to GPIB card. This card will not rely upon any specific instruments ability to actually supply power to it.This might sound excessive but consider this, it is far easier to hook up to multiple ports at a switch than it is to get functional RS232 ports or whatever. It is a question of how you will plug all these instruments into a computer, you could use some sort of RS485 implementation but I don't see an advantage over Ethernet, especially if you leverage the hardware out there to support POE. With a little bit of effort your card could bridge to instruments with only an RS232 interface and of course you will be immediately ready for instruments with Ethernet built in.As for are you nuts, not at all. I would not take the approach you are suggesting mainly because in the world of instrumentation, GPIB is legacy. Legacy isn't a bad word here just that you likely would not be going out to buy NEW hardware and demanding a GPIB interface. Rather you would be after NEW hardware that has Ethernet. Frankly a good portion of the used market will have hardware supporting Ethernet these days and if it doesn't have that. it likely has plain old RS232. So if you are going to build hardware to support legacy equipment why not make it work well with respect to a modern lab.

author: GumpyGus
author_rank: Newbie
timestamp: June 24, 2022, 03:52:13 pm
content: Thank you all. Now I can't decide! Parasite power might be feasible, or not depending on how much power and what duty cycle the wireless module sucks up. Then again Ethernet=powered is a slam dunk in so many ways-- no worries about power, no worries about BlueTooth packet collisions, simpler software that doesn't have to keep powering up and down, the ability to stay awake all the time and instantly respond to wireless messages, and probably more.I think I will at least *try* the parasite approach, just to test my lacking low-power skillz. ( My first computer was a CDC 6600, 90 Kilowatts, 400Hz. It didn't have ANY power-down options short of the Big Red Switch. )

author: wizard69
author_rank: Super Contributor
timestamp: June 25, 2022, 06:35:45 am
content: Developing skills is often the best reason to pursue a project. Sometimes you need regular practice.I liken this to my welding skills. It looked like Crap the first time I welded something up. However if you come up with excuses to weld up more projects, pretty soon you are producing good looking, strong welds. Maybe not professional grade but certainly sound.I only mentioned PoE because with all of the hardware, out there already, the project would be largely software. Add to that the flexibility to mix and match all sorts of electronics and it seemed pretty viable.

author: Kleinstein
author_rank: Super Contributor
timestamp: June 25, 2022, 07:22:19 am
content: Depending on the test instruments, they may not like the extra EMI from a couple of bluetooth modules. So a cable based (thinner than GPIB) solution may be better.Instead of POE one could in principle also consider the much hated USB.If it is just the thick cables: in the old days there were sometimes also solutions with just ribbon cables - more flexible, but with possible EMI porblems. It is however a long time ago I have seen those. AFAIR this was with old Commodore computers that used GPIB to connect printers, external floppy drives and similar.

author: GumpyGus
author_rank: Newbie
timestamp: June 25, 2022, 02:51:25 pm
content: I have tried using flat-cable and crimp connectors, with poor results. Anything more than two 4-foot lengths and the data comm is iffy. So I gave up on that. Thanks.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: June 25, 2022, 03:46:47 pm
content: Using wires ain't too bad, once you realize every way you go is some form of compromise. With RF you both have problems with stealing power and with data reliability over the air.My own preferred way is to a wired RS485 network which uses two wires for 24Vdc power and two wires for data, and then use microcontrollers to translate the data where needed. for normal runs I use regular CAT-5 cable, but for patch cables I use just 4 wires woven together and without an external mantle and this makes them supple enough for bench-top use. I could go with multi strand and silicone insulated wires but I have not had a need for that.