rather then dig up the old thread i decided to start a new one.
I had to
dig up the old thread because I couldn't understand this fully without it. It seems that this machine will be based on an ATX power supply.
[SCHEMATIC]
Your schematic is both messy and cramped. It's more cramped than it is messy (IMO), so it shouldn't be that hard to clean up. But you should also make more use of named nodes so you don't have lines going all over each other. Also, the components should be labeled with reference designators. They make the circuit much easier to talk about, so people would be more willing to help you.
In the schematic, you have USB type-B sockets, whereas on the panel you have type-A (which is what you want).
The third of the four panels with switchable polyfuses has only two current options, not three. I presume this is because the 7809 can't supply 6 A. In the old thread, there was much talk of pass transistors, so I know you already know that's an option if you want more current from that channel.
For the modules on the right, why not put switches on their power inputs if you want to be able to turn them off? The switches in series with the output relays seem strange.
[PANEL DRAWING]
Let me see if I can understand your front panel. Labels would help. You might not need them yourself, but maybe a friend will use this power supply at some point, or maybe you'll put it away when you get a better one, and pull it out years later to use for something, and not remember what does what. I would understand
none of the front panel if I couldn't look at the schematic simultaneously, and I would only understand 75% of it if I hadn't read through your old thread fully.
Anyway, here's how I interpret it. Everything I don't understand or get wrong in my interpretation is probably something you need to correct.
Column 1:Power Good LED
master power switch
button for manual relay output
LED that isn't in the schematicexternal control input for manual relay output (the "unspecified 2-pole connector")
manual relay output switched ground terminal—see below on using relays to switch groundpointless LEDs that will always be on
USB ports
Column 2:4 pairs of RGB LED and switch for the switchable current-limiting polyfuses for the 4 switchable-current-limit positive channels
Column 3:4 voltage/current displays for the 4 switchable-current-limit positive channels
Column 4:4 positive terminals for the 4 switchable-current-limit positive channels
Column 5:4 ground terminals shared between the 4 switchable-current-limit positive channels and the three negative channels (all grounds common, but one per row for convenience)
Column 6:2 yellow terminals together for the thermometer's external input
3 yellow terminals for the negative channels
Column 7:LED that isn't in the schematicThermometer internal/external switch
Thermometer display
Three voltmeters for the negative channels
Three LEDs to indicate polyfuse states
Column 8:DPS module
Relay timer module
4–20 mA semi-arbitrary waveform generator (a strange choice)Column 9:Switch that isn't in the schematicGround terminal—where's the positive output terminal of the DPS module as shown in the schematic?Switch for the relay timer
Switched ground terminal from the relay timer—see below on using relays to switch groundSwitch for the function generator
Switched ground terminal from the semi-arbitrary waveform generator—see below on using relays to switch ground and on using a relay on the output of the function generatorWhy do you have voltmeters when the voltages should not vary by a large enough amount to register on them? (Do you think you need them to know which channel has which voltage because you don't know the concept of labels?)
ok so the plan right now is to have multiple poly switches to switch between,
so i can access somewhat higher currents without removing protection altogether
or limit the current to 100ma for sensitive projects.
Using switchable polyfuses for current limiting is strange, but it could work. (I would find this power supply inadequate for testing LEDs, though. For those, I usually set a current limit of 20 mA and a voltage around 4 V and hook up the LED in both directions until it lights up (because I can never remember the polarity indicators). When I figure out the correct polarity, it runs in CC mode at 20 mA (which is a safe current level for most LEDs). I set the voltage to 4 V so that when I hook up the LED in reverse, I don't exceed its reverse breakdown voltage and destroy it.)
these will be followed by an RGB LED so the colour will tell me which fuse i am set to.
i think i need those diodes to keep from lighting up all leds all the time.
i assume these diodes would need to be rated for at least the 6A of the heaviest poly fuse
Yes and yes. On the 100 mA polyfuse, won't the LED take up a significant amount of that current?
the third relay is simple a pushbutton and a connector in parallel so i can connect a remote button or switch
or something like that. it could be used as a dead man's switch or sometimes i imagine i will want to conveniently
switch things on and off without having to reach for the unit, or give short bursts of power to test something or other.
is a relay the appropriate choice for this?
A relay is fine for that, but you've connected its switch to ground. When you press the button, the relay output will be connected to ground. When you release the button, the relay output will be unconnected (floating). I initially assumed that this is not what you want. Then I realized it probably is. You're probably planning to connect your load between whatever positive voltage terminal you want and this switchable ground terminal. This seems unwise—it will leave your whole load floating at the positive voltage when the relay output is off. If a grounded part of the load touches a grounded object on the bench, it will still be powered when the relay output is "off".
a simple signal generator […] will be included in the box.
i was thinking of having [it] drive a relay
A relay is
not fine for that.
In fact, that's probably the worst possible thing you could do there.The
function generator that you linked to in the other thread is actually an arbitrary waveform generator, which would seem like a good thing, but it's actually an
extremely limited one. It's meant for testing PLCs by simulating a sensor that provides a 4–20 mA proportional output (which is an
industrial de facto standard for that stuff). Also, it can only do 9 linear segments of a function (though that would be enough for you most of the time).
I can't tell whether it pushes the set amount of current through the current loop, or just allows the set amount of current through itself under an externally applied voltage (which would come from the PLC, in its intended application).
I can't figure out what the hookup diagram on the product page means, either. And the textual description of how you operate it makes it sound like it will be extremely frustrating to operate.
Anyway, assuming you can hook it up and get it to work, it will give a current output, not a voltage output. The current will vary between 4 and 20 mA. This is probably not suitable for driving a relay, but you haven't provided a part number or datasheet for the relay, so I don't know how much current its coil needs.
Also, are you aware that relays are either on or off, and cannot provide a proportional output? Knowing that, it makes no sense to use one as an output stage for a function generator. If the function generator could drive the relay, most of its purpose would be wasted because the relay could not reproduce the proportional output of the function.
Also, the relay has hysteresis: it requires some level of coil current to close the switch, but then when the coil current decreases, the switch doesn't open again until the coil current reaches some much lower level. This will distort the timings of the function as well.
Also, switching a relay rapidly will wear it out quickly. However, this doesn't apply to your unwisely chosen function generator because its minimum time per segment is 1 second.
A much better output stage for this function generator would be a transistor. Either a BJT or a MOSFET could reasonably be made to work. However, if you want to do that, post the schematic for review before you build it!
the thermometer would have a switch between an internal sensor and a set of binding post so i can use it externally.
i was thinking i need some thermal insulation to keep the temp inside the box from throwing off the thermometer.
maybe some of that expanding insulation foam?
Huh? What's the purpose of the internal thermometer? If it's to measure the internal case temperature of the power supply (to check whether it's overheating), just put it in there, probably in the exhaust air stream. If it's to measure the room temperature, put it in the intake air stream. Insulation would just make its readings meaningless.
also: any tips on how to wire this in an organized fashion?
Maybe make a wiring diagram first. But before you can do that, you'll need a schematic that's correct and ideally also easy to read. Dave has a video on that:
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