Half a YAPP - mini-mast display

AngusMcDoon said:
I don't think prv intended mounting it outside, so it could go in any old box or even a cout-out somewhere near the chart table.
Click to expand...

Indeed, it will actually end up glued into a nicely routed pocket in a sapele board. I may be a bit rusty on the electronics, but neat mountings and panels I can do:

6BD5BA81-2A66-46BB-BFC0-84A4358E2F43-2977-000005729F5A249B.jpg


Pete
 
To everyone whom I've sent the schematic/sauce code to, there's a mistake on the circuit diagram that's been pointed out to me. Where it says 3.3V, it should say 5V. 3.3V is not required anywhere in this design. Copy and paste error. I blame the cat.
 
AngusMcDoon said:
Where it says 3.3V, it should say 5V. 3.3V is not required anywhere in this design. Copy and paste error. I blame the cat.
Click to expand...

I hadn't even noticed that. I'd spotted that there was only the one regulator, so it must be all at 5v, and I just mentally substituted any connection like that as "the positive rail" without noticing the actual value :)

I've been working out a layout for the bits on veroboard. First time I've ever done it, so probably not the most efficient of designs, but it does fit into the same footprint as the display board which means I can repurpose the little plastic box the display came in as a case. I believe I have some second-hand veroboard in the shed with someone else's half-built circuit in one corner, but enough unused area to lop off for this project.

(PIC hasn't arrived yet so preparing the board is about all I can do. Will probably solder it up tomorrow night.)

I also plan to use the backlight on the display. Briefly considered wiring it up to one of the spare pins on the PIC (I think it can sink enough current to drive it directly?) but I decided to keep things stone-age and just wire it up to the 5v and 0v rails via a switch. Not sure whether it's supposed to have any other components, but it didn't instantly let out the magic smoke when I put the bench power supply across pins 15 and 16, and there are some resistors in series with the pins...

Pete
 
This is the datasheet for the display...

http://www.cstech.plus.com/ebay/4_line_display.pdf

The backlight takes 110mA typical, which is too much to be driven by a processor output pin, so a cheap transistor switch would be needed. It can be safely connected to 5V, but I would expect it to be too bright for a boat at night, so would benefit from a resistor to tone it down a bit, and save some battery power as well.

I was considering modifying the design so that the backlight came on on alternate power cycles negating the need for an external switch, but not done anything about it so far. The last light state could be stored in the PIC's on-chip non-volatile memory.
 
AngusMcDoon said:
The ST M4 Discovery board has audio capability, so that gives me an idea for a really pointless pointless project.
Click to expand...

It wouldn't be pointless if the voice was used for alarm purposes - depth, and off course for example. Be better than a warning bleep which has you diving for the display to see what's going on.
Just avoid boring messages. I suggest "we're doomed" for the depth alarm....
 
AngusMcDoon said:
The backlight takes 110mA typical, which is too much to be driven by a processor output pin
Click to expand...

I'd found the datasheet and knew it was 110mA; I remembered a figure of 200mA for (at least some) PICs. Turns out that's the total available from all pins though; each individual pin can only do 25mA.

AngusMcDoon said:
It can be safely connected to 5V, but I would expect it to be too bright for a boat at night, so would benefit from a resistor to tone it down a bit
Click to expand...

I'm solving these problems by brute force again - was going to use a pushbutton switch so you only turn the light on when you want to look at it, like a 70s digital watch :D. It's not something I would sit and casually monitor, especially at night - more like popping down on the hour to put the plot on the chart, and I need the log reading to write next to it.

I might try adding a resistor as well; will have to try it out in situ to see whether the light really is blinding or not. I had to order a bag of variable resistors for the contrast so could use one of them.

AngusMcDoon said:
I was considering modifying the design so that the backlight came on on alternate power cycles negating the need for an external switch
Click to expand...

Cunning!

Wouldn't really work for me though, as I plan to have it powered off the "sailing instruments" circuit (basically means Seatalk displays and the autopilot) with no additional switches. Would be rather disconcerting up on deck if someone kept switching that circuit on and off just to change the lighting on their display :)

I went out to the shed this evening to assemble the board, but it turns out I don't have any actual veroboard after all. A couple of sheets of perfboard with holes but no copper, and a big sheet of odd stuff consisting of strips of copper but no holes!

To get something done, I did solder a row of header pins (out of an old ribbon cable socket) onto the display board, ready to join the two halves of the sandwich together.

Veroboard now on order.

My mate is dead impressed that it's possible to build the functional equivalent of a £400 display for under a tenner :)

Pete
 
The Ebay supplier I linked to only has 2 displays left and won't be getting more. However, RS part number 720-0210 looks identical. The SPLC780D driver chip is compatible with HD44780.
 
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Hmm, interesting.

An S100 autopilot remote is on my list of things to add. If there's a potential YAPPish equivalent in the works then I'll have to hold back on that.

Packaging would be more of a challenge, of course. But I'm sure I could come up with something.

Pete
 
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