SOC-Meter Kit Hardware, Display, and Issues

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SOC Meter, proposed (intended, not "promised") Physical Configuration:

My latest thinking, that I will try to build today (or Sunday), even though I still lack suitable sub-miniature pushbutton switches (n.o., momentary close) to use for the User-Input.

1. A black plastic box, about 4" wide x 2" high x 1.7" deep. The "cover" to the box forms the back face, secured with 4 small hex-head recessed screws, for easy-access to the firmware-update connector.

2. Front Face: A Four-Digit, 7-Segment LED Display, centered in the face.

3. Bottom and Right Side: No holes.

4. Top: Two holes "closer" to the front edge to mount the two User-Input (momentary close) pushbutton switches.

5. The Left Side: A notch in the back edge for the incoming 6-foot, 16-conductor cable from the right-angle OBD connedtor. Two mounting holes for 3-position toggle switches:

a. A single pole for Power "always On", Off, or "Auto-On" (when the car is "Ready").

b. A double pole for "EV-CAN buss" (SOC Mode), "No CAN buss" (Setup Mode), and "Car-CAN buss" (Tire Pressure Mode).

Possibly two small holes low on the side and two small holes high on the side if needed for cooling (I hope not, since it only uses about 1.5 to 2 watts).

Any thoughts or comments before I begin "mass" production (one prototype :D)?
 
garygid said:
4. Top: Two holes "closer" to the front edge to mount the two User-Input (momentary close) pushbutton switches.

Possibly two small holes low on the side and two small holes high on the side if needed for cooling (I hope not, since it only uses about 1.5 to 2 watts).
Click to expand...

I wouldn't make any holes you might not end up using.
 
OK, for my v1.02 SOX-Meter:

1. I added a 5.1v 1-watt zener diode and that appears to work well.

2. I added a SP On-Off-On power switch. Since I discovered that the OBD's Switched Power is ON in the second ("full") Accessory Mode, the Auto-Power seems good for most. However, being able to easily switch the SOC-Meter On anytime (while charging), is good for me.

3. I added the DPDT (I used a DP On-Off-On) switch to select the EV-CAN buss or the Car-CAN buss, but I have yet to decode something useful from the Car-CAN buss.

I still need to find some good, small, sub-mini pushbuttons at a good price.
 
For two User-Input push-buttons:

1. One package of four SPST mini Pushbutton Switches (2 black cap and 2 red cap, momentary, normally open) from Radio Shack (275-1547) is $3.69 + tax.

2. We will install one Red and one Black pushbutton in the "top" surface of the SOC-Meter box, centered over the display, near the front edge of the top, spaced about 13/16 inch center-to-center (3/4 to 7/8 inch is fine).

3. Carefully bend the solder lugs out at right angles so the lugs are less likely to touch the display card.

4. After soldering three wires to the switches (one common, for Ground, and a wire for the "Red" switch and one for the "Black" switch) and installing the switches, put a piece of electrical tape over the lugs and the switch bodies to help avoid unwanted shorts on the display card.

5. Looking at the meter face, put a Red cap on the left button, and a Black cap on the right.

6. These 3 wires will probably connect to the EXT2 connector.

Different button-pressing sequences will select various operating/display modes for the Meter.

Initially, the Black button will simply toggle the display between NNN "raw" SOC and the NN.N percentage SOC (based on 281 raw = 100%).
 
My preference would be to use one of the larger displays and show multiple values at the same time. I'll work on it once I get the LED one is working first ...

BTW, Gary, the avr-can has a "user button" feature listed. What does that mean ?
 
The AVR-CAN has two on-board buttons, one connected to Reset, and the other (called BUT) for the programmer to play with.

In spite of its "robust" name, BUT is small and a bit difficult to press.
 
I just added an SOC-Meter project Parts List to the first post.
About $100 in parts for one SOC-Meter.

For anybody interested, I will soon have (or had):
1. one SOC-Meter Kit available for about $150, or
2. a completed SOC-Meter for about $250 (takes time to build).
 
Regarding what "range" to show, I've seen several posts asking for what seems to me to just be additional variations of the built-in guess-o-meter. That doesn't seem very useful to me, as I drive mostly in the city, and sometimes on the highway, at varying "burn" rates. How I've been driving the past few minutes, miles, days, or weeks will often have little correlation with how and where I may be driving next.

What I think would be nice is a min/max range display. Not guestimates.

The problem with the guess-o-meter is that you never really know if it's currently showing you something closer to "min" (worst-case, meaning it could be much better/higher) or "max" (best-case, meaning it could be much worse/lower).

But if the battery is at, for example, 50% SOC, then why not simply show "35-50" as the range (or to fit in four-segments, maybe "35:50") ?

The max (100% SOC) high/low range could default to some typical values like 70 and 100, but could (in setup mode) also be adjusted to fit your needs. But the display would then be able to tell you what your min/max would be for a SOC like 43% without you having to calculate it yourself.

Let ME decide if 35:50 really means 35 or 50 or somewhere in-between, as only I know if I'm going to be driving city or highway, and knowing the range, I can decide if I can "splurge" on A/C and fast driving, or if I need to economize to ensure I can complete the trip. This is the part that is difficult with the current guess-o-meter because we don't know what mi/kWh it's currently assuming, or when it might suddenly change.

But we know the SOC, and we have a pretty good idea of best and worst case range so I think we could display a pretty useful range that empowers the driver to decide how to drive based on how far you're going.
 
By the way, I'll try to remember to mention this at the BayLEAF meeting in a few hours (is it really almost 3am?), but if folks in the (south) Bay Area would be interested in doing a group purchase of kits or components, or even just getting together somewhere to assemble and program them (Hacker Dojo perhaps?), let me know (pm here or email me directly or on the BayLeaf list).
 
Display Color Preference:

Which color is "best", or is it mostly a preference item?

These small 7-segment, 4-digit LED display modules come in 4 colors, Red, Green, Blue, and Yellow. Some colors might be more available than others, but when I first ordered, I bought one of each to evaluate.

I have yet to see a Red or a Green Display operational, so I do not yet have an informed answer to "best".

So, I will try to power up all 4 together (requires a regulated 5v DC) and observe them in various lighting conditions.

Generally they are almost "too bright" in darkness and almost "washed out" in direct sunshine.

I could program the latest SOC-Meter (which has the 2 user input buttons) with some number of levels of brightness control, and that solves the night-time (slight) problem, but the full brightness is certainly needed (according to my eyes) for strongly lighted (sunshine) conditions.

Opinions/experience?
 
garygid said:
Generally they are almost "too bright" in darkness and almost "washed out" in direct sunshine.

I could program the latest SOC-Meter (which has the 2 user input buttons) with some number of levels of brightness control, and that solves the night-time (slight) problem, but the full brightness is certainly needed (according to my eyes) for strongly lighted (sunshine) conditions.
Click to expand...
Doesn't it depend where you mount the display? I'm a fan of large (and few) digits for the SOC, to make it easy to read at a glance. Displays with more chars might be nice, but they'd typically be smaller and require more attention in order to read them. This likely leads to putting it closer to the windshield, which I'm guessing leads to the "washed out" problem in bright sunshine.

But going back to just a few, large digits... someone mentioned putting this down in the tray below the dc power outlet (forward from the shifter). Is this still the plan or are you thinking of mounting it somewhere where sunshine is likely to be more of a problem?
 
An LCD display usually has either:
1. a lot of power for a backlight, or
2. Low contrast
but has the advantage of more characters.

To get started, I have chosen a high-contrast solution:
A 7-segment, 4-digit, LED display with 10 mm (0.39") high characters that can easily be read even from outside the car.

Placing the SOC-Meter box (lees than 4" x 2" x 2") on the shelf between the USB and AUX-AUDIO ports works well, and is usually well-shaded.

However, it can also sit on the flat area above the NAV screen, but can get more sunshine there.

The 6-foot cord from the LEAF's OBD port gives quite reasonable flexibility, I believe.
 
I don't think power is an issue, since it's not running on batteries. The current draw is really minimal.
Though I haven't checked any spec sheets, I'd be surprised if a large, bright LED display drew significantly less current than an LCD.
But it's probably easier to source a large LED than an LCD with large characters.
The displays in BMW's are all LCD, and they have plenty of contrast. I have a cheap $7
one connected to an arduino with a white backlight that has plenty of contrast.
Some of the 2-line models allow custom bitmaps, which would allow you to display 2x height
characters.

You might need to add some sort of automatic brightness control to your LED to prevent blinding or distracting
the driver at night, depending on where you choose to mount it.

BTW, I noticed a lot of auto manufacturers use orange/red lighting on their gauges.. so perhaps red would be the best
color to use. There must be a reason that they pick those colors... maybe less eyestrain at night?
 
Green is often good for daytime, and Red is often used at night, as better for the eyes when they are trying to accomodate to more-sensitive night-vision.

With the lights encountered in normal driving conditions, the eyes probably never accomodate.

A perception of "yellow" can be from a combination of a Red wavelength and a Green wavelength, but a Yellow LED only outputs one in-between wavelength.

So, some testing is in order.

Some people see some colors better than other colors.

If you have a good LCD display, please give us a link directly to it at a source. Thanks.
 

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