cheaper large instrument displays - mast mount

The data sheet from RS doesn't say what you're actually supposed to do with the contrast control input. It just shows a vague indication of a variable resistor between VOUT and VO. Not even a suggestion of suitable value! Is there more info somwhere?

Having said that, is there really any reason to make the contrast user adjustable? It's not like the backlight brightness - needing adjusting as conditions change, or the "contrast" on a TV - as we're not dealing with greyscale images here. As far as I recall, the contrast control needs optimising for best viewing angle, but after that can be ignored. Of course, there may be temperature effects, but with backlighting on at a fairly high power (for daylight reading) it's not going to get too cold.
 
The datasheet, like most datasheet for this sort of stuff from China, is complete rubbish. I have the previous incarnation of this display from RS, and although a different model, the connections and the hardware driver chip on the panel are the same. The datasheet for this older model shows that a pot should be connected between Vout and Vdd with the middle terminal going to Vo, the control input. I expect the datasheet for the new model is wrong and the old way is how it should be connected so that an adjustable voltage level between Vdd and Vout is piped into Vo.

I don't know whether a user control of contrast is required for this display, but similar previous displays I have used do need it if they are used in a temperature range outside of standard room temperature, i.e. 0C to maybe 40C as found on a boat.

Contrast control can be left for later, as long as the chosen microcontroller has suitable outputs, which the STM32100 does. For now a pot will do.
 
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nigelmercier said:
Need someone who does analogue; if nobody here, I can ask some analgeeks. What range of negative volts do you need?

[Later] does the LCD not have an application note?
Click to expand...

I don't know until someone gets one and sticks it in the freezer/oven and does some tests.

Couldn't find anything on Displaytech's website other than the datasheet and the 8051 driver source.
 
AngusMcDoon said:
The datasheet, like most datasheet for this sort of stuff from China, is complete rubbish. I have the previous incarnation of this display from RS, and although a different model, the connections and the hardware driver chip on the panel are the same. The datasheet for this older model shows that a pot should be connected between Vout and Vdd with the middle terminal going to Vo, the control input. I expect the datasheet for the new model is wrong and the old way is how it should be connected so that an adjustable voltage level between Vdd and Vout is piped into Vo.
Click to expand...

That makes more sense. In that case, a simple inverting op-amp circuit between the DAC output of the uP, with gain and offset worked out suitably will be easy. Suggest TL061 or equivalent as cheap, low current (althought not quite rail-rail, probably Ok). Power from Vout and Vdd with non-invert input connected to 0V, 3 resistors to set gain and offset and it's done. A bit of experimentation will be needed to find a default contrast voltage - so you can see the display when you first switch it on, before doing any setting.
 
i had a delivery of some sample enclosures today

First up is the tekmag - aluminum, looks good and well built giving a quality feel, waterproof to IP67 (although we need to get a hole cut for the LCD etc) might be quite a good starting point.

http://www.teko.co.uk/en/prodotti/famiglia/AL/serie/133

I also had this one delivered as to see what it was like

http://www.teko.co.uk/en/prodotti/famiglia/HH/serie/87

again, quite nice but not waterproof out of the box, feels a little plasticky but better than most, has a decent depth of 40mm

I also had a 4 button remote housing delivered should we choose to go this route, looks good, feels quality and waterproof

http://www.teko.co.uk/en/prodotti/famiglia/PO/serie/134


any initial thoughts?

i will go back and speak with them about customisations etc with regard to colour, cutouts etc etc, they offer a full customisation service
 
I've used the "remote" enclosure - you can just about fit a 433MHz transmitter module, button cell holder and one of the smaller PIC processors inside, along with at least 1 switch (my application only needed 1) inside. I think I found a slightly better enclosure - I'll try to find out which one it was.

The other enclosures look good, although they are really intended for hand-held applcations - hence the "rubber" sides. You will need to think carefully about how to seal a window for the LCD into the front. Probably thin perspex (or polycarbonate, as it's tronger) stuck with araldite. Use a self-adhesive overlay to hide the glue and provide front panel graphics logo etc.
 
Thanks mike

I did email temp this afternoon asking for their thoughts on maximising and sealing a screen for a LCD, their response was very helpful, 'give us a couple of days and we send some drawings' I will await their ideas.

The rubber mountings on the aluminium case are fairly unobtrusive and can be removed form the design of required...still thinning about how one of these could be mounted. The hand held enclosures seem to be the best looking items, I guess everything is a compromise on cost initially..hopefully a moulded CSS maybe possible in the long term

Anything you have for a remote (should we go this route) would be much appreciated.

I reckon the teko enclosures are close, but not quite there and may require some significant machining..I will keep looking and have requested a couple of other samples. I do have a call about moulded sheet later this week with one of your other reccomendations, thank you for those
 
I've not tried araldite with polycarbonate, but superglue sticks it well (just don't get smears where it's not wanted!). The reason I suggested araldite is to provide a seal, as well as sticking it dowm.

I'll try to dig out what I did with the remote case, and see if I have any photos. I can't remember what wasn't quite right about that case - I seem to remember the main problem was wanting to attach it to a lanyard, and the hole being too small (or the case too thick at that point). I also had doubts about it being sufficientlt waterproof - I think there is a hole for a LED, but it's not covered.
 
I've found the prototype that I made for the remote - it would appear to be the previous version of the case - the one you are looking at will probably be better. My device uses quite a large (relatively speaking!) battery, as it needs to operate continously, so the battery takes up most of the reverse side of the PCB. I would imagine you could use a smaller battery, allowing the transmitter to be on the reverse side instead, allowing more space for switches.
 
nigelmercier said:
Use a light pipe, bonded to the case. Cut a rod to size and polish the ends. Also gets rid of the need for LEDs on stalks.
Click to expand...

Having looked again, I think the ones Shaun posted have one bonded in, so they're better sealed than the one I tried. I did, after I built the prototype, get sent details of the other one and decided it would be better, but I don't seem to have a sample (the project has been on ice since, anyway).
 
The driver for the 240x128 display is going. This is the old RS display, but it has the same interface as the current one.

SDC11528.jpg


SDC11531.jpg


SDC11530.jpg


Backlight control is working using a PWM output driving a MOSFET, although I can replace the current large power MOSFET with a smaller cheaper one.

SDC11529.jpg


Contrast is controlled at the moment using a 10k pot, but I have not found a suitable circuit yet for software control. I tried an op-amp in inverting mode, but as soon as I connected the negative power rail of the op-amp to the negative voltage output from the display, the generated negative voltage output went up 5 volts (i.e. -18V to -13V). It looks like the op-amp was drawing too much power and partly grounding its supply.

I tried another suggestion of connecting the DAC output to the top of the 10k pot and setting the contrast with the pot to mid range. Varying the DAC output I could vary the contrast slightly, but not by enough. The voltage divider effect was reducing the DAC's 3 volt swing to less than half a volt.

I also tried just using a single NPN BJT, and I got near, but couldn't get the voltage swing on the output big enough. It needs someone who knows how to bias the transistor into its active range.

These are the volts available and needed...

Negative voltage generator output: -18V
Contrast adjustment voltage range: -13V to -15V

Software using buttons (rather than a remote control) is well advanced. There are 25 NMEA channels that can be displayed so far and about a dozen Seatalk ones. It is possible to go on adding NMEA channels pretty much forever as there are so many variants, although SRAM resource with the current processor will soon limit more additions. This is the list so far...

"BOAT SPEED KNOTS"
"DEPTH METRES"
"DEPTH FATHOMS"
"DEPTH FEET"
"COURSE OVER GROUND"
"SPEED OVER GROUND KNOTS"
"CROSS TRACK ERROR"
"WINDSPEED TRUE m/s"
"WIND ANGLE TRUE"
"TRIP DISTANCE NM"
"WINDSPEED TRUE KNOTS"
"HEADING"
"WIND DIRECTION MAGNETIC"
"VELOCITY MADE GOOD"
"WIND ANGLE APPARENT"
"WINSDPEED APPARENT KNOTS"
"WINDSPEED APPARENT m/s"
"WIND DIRECTION TRUE"
"TOTAL DISTANCE NM"
"BEARING TO MARK TRUE"
"SET TRUE"
"DRIFT"
"DISTANCE TO MARK NM"
"BEARING TO MARK MAGNETIC"
"SET MAGNETIC"

The memory resources on the processor are getting near their limits. It will be possible to use the STM32F100RB as found on the Discovery board with no further software expansion, but if a custom PCB is made we should use the STM32F100RC; for another 20p it has twice the flash and 3 times the SRAM. This will allow future expansion. I expect the pinout is the same although I haven't checked.
 
non-electronics person here, just keeping tabs on this as a potential customer, so please bear with silly questions.

If the case is magnesium or aluminium alloy, is there any issue of corrosion or stray galvanic currents if it is fixed to the mast without serious insulation ?

Also if covered in seawater spray ?


Otherwise, most impressed with the Marine Electronics Co-operative :)
 
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