In car multigauge

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RogerClark
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Re: In car multigauge

Postby RogerClark » Sat Mar 11, 2017 9:01 pm

With the buttons, if you can switch the input mux fast enough, the buttons will not get blocked.

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BennehBoy
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Re: In car multigauge

Postby BennehBoy » Mon Mar 13, 2017 6:28 pm

While I wait for some parts to arrive that will allow me to connect up the spare ECU to the project, I started to think about how best to power the ECU on the bench.

I'll need to simulate an ignition switched relay turning on the main power which should be fairly straightforward, but I don't have a bench PSU...

So, I started converting a spare 650W ATX PSU into a bench supply, it's pretty straightforward, the only thing to keep in mind is that the highest rated output needs a dummy load in order for the voltages to be stable. In the case of this PSU it's rated like this:

+12V1 - 23A
+12V2 - 23A
+5V - 40A
+3.3V - 30A
-12V 0.8A
+5V/SB 3.0A

I've got a couple of 10W power resistors coming in the post that I'll load onto the 5V line (although I'll probably hook both 12V outputs into one rail so that will techincally be higher output).

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zmemw16
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Re: In car multigauge

Postby zmemw16 » Mon Mar 13, 2017 6:47 pm

isn't there a pin in the big connector to a mother board to switch the psu output to on/off ?
might be nicer than toggling the mains switch to the psu
stephen

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BennehBoy
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Re: In car multigauge

Postby BennehBoy » Mon Mar 13, 2017 6:52 pm

zmemw16 wrote:isn't there a pin in the big connector to a mother board to switch the psu output to on/off ?
might be nicer than toggling the mains switch to the psu
stephen


Yes, green wire is at +5v, pulling that low to ground powers on - I'll be fitting a rocker switch in the hole where the cables used to exit.

Also, there's a purple +5v Standby line, I'll pop a red LED on that to show that the rear switch is on. Then will have a green LED driven from the main +5V to show 'ON'.
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RogerClark
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Re: In car multigauge

Postby RogerClark » Mon Mar 13, 2017 7:55 pm

Which outputs do you need to connect to the dummy load resistors ?

BTW. i have one of those cheap'ish, 0 - 30V 1A variable PSUs, which also has a variable current limit; and I find it very uswful.

However sometimes 1A isnt enough, as the current regulator can kick in durimg initial surges, so i think I will need to build something like that PSU for when I need more current in either 5 or 12V

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BennehBoy
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Re: In car multigauge

Postby BennehBoy » Mon Mar 13, 2017 8:30 pm

All of the online tutorials suggest to connect the load to the highest current output - specific load power rating/resistance depends on the voltage of that output.
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RogerClark
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Re: In car multigauge

Postby RogerClark » Mon Mar 13, 2017 11:43 pm

Umm. Not sure if the 5V or the 12V need to be loaded in that case.

I did read somewhere that the 12V needed load for the 5V to work,or perhaps it was the other way around.

But that may no longer be true.

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BennehBoy
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Re: In car multigauge

Postby BennehBoy » Mon Mar 13, 2017 11:54 pm

I've run these with just the 12v line with a load connected with no issue. Probably worked OK on this one because the 2 12v rails total up to 40+ amps
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RogerClark
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Re: In car multigauge

Postby RogerClark » Tue Mar 14, 2017 4:20 am

OK... Thanks.

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BennehBoy
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Re: In car multigauge

Postby BennehBoy » Tue Mar 14, 2017 12:28 pm

Took a few minutes this lunchtime to get the 74HC154 Demux into the equation.

A scant few lines of code changes to the adafruit_ssd1306 library and it's now working.

There's no method within the library to clear all the outputs so for now I'm just writing an out of range line active to clear the CS lines on my screens. When I get a moment I'll fork the library on github and add a clear method that simply sets E1 thus disabling all the outputs.

So that's freed up 3 GPIO's, which means I now have working SD & a luxurious 2x unused GPIO.
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