Hi,

I'm looking to obtain what is essentially a stopwatch, the sort you can buy for $10, but the display needs to be visible from 300 feet away. It's for an athletics club, but we don't have the $$$ it takes to just buy one, $500 - $2000.

So I'm looking to make one, and I'm open to any creative suggestions. I have limited electronics knowledge but did it a bit at Uni (did Physics) & I can follow instructions. My constraints are the solution must be simple and cheap.

For display, a 5 digit 7-Segment 10" LED will be fine. Hunting around they are expensive. However I can buy a 24cm strip of 24 bright white LEDs for $2, so for $14 plus a few resistors and some black backing; I figure I can make a common anode or common cathode simple 7 segment display. So for under $100 that solves the display problem.

Next I need to control them. I had imagined that I would take an existing stop watch, connect to whatever controls the 7 seg display, put in some sort of switch-able current source with an Op Amp for each segment, and voilà. I've found out it's not as simple as that though. My $10 LCD stopwatch does not raise pins high and low to control each segment as I had thought it would. (I stripped out down and used a multi-meter to check).

So I'm looking for suggestions. I've thought of:
1. Buying a $20 LED timer and hoping it will let me control my giant LEDs with some Op Amps in between (one for each segment). This sounds fraught with pitfalls, I think that the odds of a commercial cheap LED timer raising individual segments high and low the way I need are low from what I've read.
2. Trying to learn how to use one of those Arduino things, but that seemed complicated. I guess I could go down that path if you guys think that's the best way forwards.
3. There seem to be various ICs made for this sort of thing with ready made instructions, looks like a bit of a learning curve though.
4. I'm happy to use a device such as a laptop or Android phone to drive the display, I'm at home with software. It's not clear to me how I would interface them though.

Thanks in advance for your consideration and suggestions.

 

...
I'm looking to obtain what is essentially a stopwatch, the sort you can buy for $10, but the display needs to be visible from 300 feet away. It's for an athletics club, but we don't have the $$$ it takes to just buy one, $500 - $2000.
...

Sorry tobe negative but to make a timer+display which can be seen well from 300 feet away (and in daylight??) is NOT going to be cheap.

You could probably come in under $500 total but you would need some expertise and a LOT of labour.

Why not do a sports club fundraiser night? Sell a few beers and some raffles and you should easily raise a couple grand for the night.

 

@ THE_RB. You may be right about 300 ft in daylight, but I'm basing this on displays like this http://www.cosyclocks.com/4digitledclock10.htm that work well with 18 LEDs per segment.

Before I run into much cost or labour I'll make a digit for $20 and see how it looks in daylight.

If this fails, then yeh I'm sunk and I'll need to pursue a solution along the lines of what you suggest.

Kindest Regards...

 

The digits are the hard part, the rest is fairly routine.

We recently had a thread where the OP basically taught himself digital electronics, and build a soccer stadium scoreboard.

Count down timer for my soccer club

My suggestion, build the digits first, the rest is cake.

Is this going to be indoors or outdoors? Wood is cheap, and you can push through LEDs though slightly undersized holes. It is basically point to point wiring.

How experienced are you with LEDs and soldering in general?

 

For display, a 5 digit 7-Segment 10" LED will be fine.

Are you sure? At 100 yards, 10" is awfully small, just 0.16° of visual arc. It's the same as just 6 pixels on my screen (100ppi) at my viewing distance of 22". Six pixels is pretty tough to resolve.

A simple, if not so cheap, solution would be to focus any video camera on an iPod timer and put the video onto a 30" HDTV screen, which you could find for under $200 (for 720p, plenty for this). Might be tough to see in sunlight, but it would be a bit bigger.

 

You can build 7seg. displays from 1W or 3W power LEDs. 3W can work from 5V electronic transformer, 2 in series, but they also need suitable cooling.

You could for instance use relays to control individual segments.

100pcs 3W LEDs on eBay = good price, for electronic transformers as well.

 

1) Why do you want to time large, cheap sports?

2) I think you are being way overly optimistic to think that 10" segments are going to be readable at 100 yards. Can you readily resolve two lines that are less than a foot apart from 300 feet away? I know I can't. Figure that people typically hold there watch roughly a foot away from their eyes when they look at it and that the segments are on the order of 0.1". So scaling that would argue for segments on the order of 30". You probably want larger than that because people want to get the numbers by just glancing at the board.

3) Keep in mind that your segments don't need to be continuous. You could build your segments as a set of discrete lights on a 2x4. Put perhaps 5 lights a foot apart on a 48" board as one segment. You can use power LEDs or even incandescents.

 

Welcome to AAC Gokiwis.

I agree with Bill. Your biggest hurdle is the digits. Bill and I have been working with the OP in the post he linked. It covers much of the same things you're looking into now for the same reasons - large displays for low cost. It is a long thread, so here are a few points that OP learned as well as my input which you may find beneficial.

• White digits don't do well - they are hard to see in daylight and hard to look at at night.
• Blue digits work well in daylight, but may or may not do so well at night.
• Red is easier on the eyes at night if outdoors.
• The human eye sees green the best, but this might be a little too intense at night depending on the brightness.
• The brightness will need to be high in daylight and dimmed at night.
• The OP from the other post discovered 20" high digits could be seen well (as witnessed by a group of end users) from 50 meters away (~160ft). You want to see from double that distance, so you may need to go bigger, but definitely not smaller.
• The link you provided to a 10" high pre-built display is neat and lists multiple applications, but note they do not tell you how far away you can see and read the digits from.
• Plan to put a filter over your display such as a dark transparent colored acrylic sheet in close to color as the LEDs used as possible.

Some questions:

1. You said five digits. In what format do you want to display the count, e.g., H:MM:SS, MMM:SS, MM:mSmSmS, etc. (H -hour, M - minute, S - second, mS - millisecond)?
2. How do you want the display to operate? Count down from some set value or count up from zero? Do you need to pause, resume, set different count down values, etc.?
3. How do you want to control the display? Wired buttons, wirelessly, photo sensor, etc.?
4. This could end up costing a few hundred dollars. We can certainly help you find the least expensive option, but what is the cap? What is the most your athletics club is willing to spend? If you say for instance $100, we probably can't help you meet all of your goals. Keep in mind you need control electronics, digits, power supply big enough to power the digits, some sort of controls (simple wired buttons or a wireless remote), and an enclosure for everything. The enclosure could well cost half of the total project.
5. I suggest taping together a few sheets of white paper and draw 1/4" thick black lines with a marker to make a 7-segment display (the number 8). Try a 20" tall digit (10" long segments) and put it where you plan to put the display (ground level, 6 feet off the ground, etc.). Walk the max distance you want to be able to see the display in daylight or with the lights on indoors and take a look. Can you clearly make out the digit? If not, first try increasing the segment thickness from 1/4" to 1/2". If you still can't make it out, try making the segments longer until you can.
6. I like the thought of using LED strips as segments, but I suggest red, green, or blue. Can you find these just as cheap?
7. Will this be indoors or outdoors? If the latter, will it be used only during the day, only at night, or both?

If you need the electronics to be as cheap as possible, using a microcontroller is the way to go, but it will involve time in learning to program but will save time in assembly. If you don't want to learn to program, this is easily done with digital logic ICs, but will require a lot more parts and assembly time.

 

Are you sure? At 100 yards, 10" is awfully small,
...

Yep! I was thinking more like 2 foot high digits for a good size at that distance. If it needs to be used in sunlight it can get hairy as the LEDs need to be really bright and you need a hood or something too, to stop the sun washing out the display.

 

This $400 timer has digits 12" high and claims to be visible at 150'. I think you can take that as the upper limit of reality.

 

Hi,

Thank you for your questions and suggestions. What I am taking from this is I need to test one digit first and make sure that meets my needs before going much further. At $20 to test this, it's good to get this out of the way.

To answer some of the points:

1. The use is mainly for cross country (outdoors) during the day, but being able to use for track would be good, so something similar to the $10 stop watches that start at "M:SS:tenths hundredths" which then changes to H:MM:SS after 10 mins is good.
2. The ability to start/stop and reset to zero with count up functionality is needed, that's all really.
3. I agree with the point about the housing possibly costing as much as the rest. If it creeps up to $400 I may as well buy the one mentioned by wayneh. I'll google for that.
4. As for 10 inches not being big enough, that's what other clubs use and they give good results, I have not measured the 300 feet but I think it's realistic. A typical LED microwave oven or radio alarm display has 0.56 inch digits and my kids can see it at 30 feet (I made them walk onto the back deck) and set the time on it, then asked them the time on the display.
5. My DIY skills are good, but my soldering lousy, I can try harder. I don't mind the hours to construct but would like it to be reliable.

The actual electronics to drive such a beast are still an unknown for me. I really wish my stripped down $10 stopwatch would work as the driver, with some simple ICs between that and the segments. Alas no one has said that may be possible.

So far I'm seeing feedback that some ICs cheaper but more work, and a microcontroller would be easier to make if I don't mind the programming - which I'm fine with.

Thanks for your help, I'm still open to any suggestions. In the meantime I'll progress to step 1 which is make a 7 seg display and test it's visibility.

Kindest Regards ... gokiwis

 

I should have given you this image of a clock used by another club. http://www.ashgroverangers.org/images/raceclock.jpg

Unfortunately we can't get the same funding they had, this particular clock was over $2000. I guess I should add $20 for the tripod stand.

 

Alas no one has said that may be possible.

Well I sort of did.

You know, any laptop with video-out could be configured to show a fullscreen clock onto a display of your choice. Some could even split the display over two displays, giving you more horizontal real estate for huge digits. The software could give you any format you want, or toggle between different formats. This could all be done without building or dedicating anything except for the mounting stands to use in the field.

 

I should have given you this image of a clock used by another club. http://www.ashgroverangers.org/images/raceclock.jpg

Wow, $2000 for that? Sheesh, I'm in the wrong business.

Okay first question, if another club owns this, can you visit them, walk 300 feet away and see if you can still clearly make out the digits?

I've been thinking about hacking a cheap timer in the same way. I've got one at home - I'll try to see if it is possible to get a voltage off the segments to power larger ones.

When you say tenths hundredths, do you mean milliseconds, i.e., 1/1000 of a second? This would require three digits which would require a total of six digits: M:SS:mSmSmS.

Or do you mean 1/100 of a second: M:SS:hShS (five digits).

Or 1/10 of a second: M:SS:tS (4 digits)?

which then changes to H:MM:SS after 10 mins is good.

To do this, you really need a microcontroller. Might be able to swing it with digital logic, I'll ponder it some.

The ability to start/stop and reset to zero with count up functionality is needed, that's all really.

Except for the note above, you can do with with a clock circuit and some CD40110 ICs in digital logic.

My DIY skills are good, but my soldering lousy, I can try harder. I don't mind the hours to construct but would like it to be reliable.

IF you decide to go with digital logic, but don't trust your soldering skills, I suggest using wire wrap. It's simple and will save you a lot of time trying to make a board or route wires neatly on a protoboard.

So far I'm seeing feedback that some ICs cheaper but more work, and a microcontroller would be easier to make if I don't mind the programming - which I'm fine with.

If you decide to use a microcontroller and want to do it cheaply and not spend too much time learning how to program, I suggest using a PICAXE: http://www.picaxe.com/What-Is-PICAXE. The hardware is cheap and it uses BASIC programming language. Arduino, while popular, uses C programming language. BASIC is much easier for a beginner in my opinion. There are many varying opinions on this subject, so don't take mine as the absolute truth. Take a look at the programming languages and see which one sees to make the most sense to you before you buy.

Let us know what you find out in building and viewing your display. Also, take a look at the LED signs for gas prices at gas stations. Gauge about a 300' distance and see if you can clearly make it out. If yes, go to it and measure the length of each segment (or eyeball it and guess) and note how many LEDs make up the segment thickness.

 

Wow, $2000 for that? Sheesh, I'm in the wrong business.

Don't be so sure. That thing is probably designed to be safe in inclement weather, to maintain accuracy under a wide temperature range, to withstand several g's of impact, and it may have a wireless remote control and RF synchronization with other race timers, and other features we don't know about. By the time you design, build, and warranty all that, for a market of what, a few hundred?, there may not be as much fat margin as it seems.