3 digit 7 segment with 4511B

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rextal

New Member
Can anyone tell me if the 4511B Cold Cathode driver as mentioned in the simple circuits manual (page 21) will drive the 3 digit integrated displays? The sample code is a simple loop so I'm speculating that instead of 0-9 you could send 0-999 to a 3 digit unit. There appears to be the same pin configuration on the 1 digit and 3 digit 7 segment displays and the datasheets tend to show they're internally connected to be externally as one device.

I'm just looking for a simple way of displaying the current stored variable. I don't need any clock or other functions.

Regards, Rex.
 
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SAborn

Senior Member
Is a Cold Cathode driver anything like a Common Cathode driver? as im not sure what a Cold Cathode driver is, other than one stored in the fridge.
 
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nick12ab

Senior Member
What are 3 digit integrated displays?

I don't just want to be told 'seven segment displays', you need to also say whether each digit has dedicated pins or if the display requires multiplexing.
 
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westaust55

Moderator
rextal said:
There appears to be the same pin configuration on the 1 digit and 3 digit 7 segment displays and the datasheets tend to show they're internally connected to be externally as one device.
Click to expand...
Please provide a link to the web page with the datasheet for the exact 3-digit 7-segment display you are using.
Without knowing which device you have and how it is conencted internally no-one can advise you with any certainty how the connect, whether to use 3 off 4511 chips or 1 x 4511 and 3 transistors for multiplexing.
 
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westaust55

Moderator
There are cold cathode type 7-segment displays - often called "Nixie Tubes".
http://archive.siliconchip.com.au/cms/A_109117/article.html
http://tubehobby.com/store.php?cat=2

Recall a local Australian electronics store had a batch for sale in more recent history.

As well as discrete driver transistors, there are even driver chips specifically for them: http://pdf.datasheetcatalog.com/datasheets/150/216759_DS.pdf

So albeit that it may be common cathode LED displays, lets wait for the OP to confirm what exactly he has.
 
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rextal

New Member
Looks like my mental auto correct got the better of me again. I did indeed mean 'common', not cold. I'm glad I was able to provide a bit of humour, definitely not offended at being made fun of it, rather the opposite actually.

By integrated I meant not 3 separate pieces of 1 digit each with 10 pins but 3 digits all in one package with 12 pins. I've seen a few items on e-bay, one being the ASR3361 however they don't have datasheets on their add and I haven't tracked one down yet. presumably you get that with the item and I'd definitely ascertain or obtain this prior to purchase. One of the vendors is someone whom I've bought a few things from and they're more than happy to provide any info like that up front.

Please note I'm fairly new to this, though the interest has always been there. So far I've only made the CD Macro rail project with adding LED's and altering the code for my needs. I'm quite confident I can do the multiplexing aspect, I saw that in the manual and it makes sense to me.

However my reasoning for questioning the number of driver chips for the integrated 3 digit packet. The single digit ones each have 10 pins and the The 3 digit one has 12 pins. This made me believe there is just one pin added per additional digit beyond one (perhaps it's one anode per extra digit). Looking at the simple circuits manual it shows the schematic of 7 outs of the 4511B to each segment on a single digit. No problem. I presume another pin is dedicated to the decimal point, leaving 2 pins (Anode and Cathode). So looking at the 3 digit unit with only 12 pins I couldn't see how you would multiplex 3 of the 4511B's to control each digit individually as it would require 21 input pins on the 3 digit display plus those for decimal and power, theoretically to me the 3 digit unit should have a minimum of 26. This got me wondering if it had the same 7 inputs for the segments, 1 for decimal points, 2 for anode and cathode and the two extra pins were for toggling high low to multiply the 7 to 21 in some fashion. The example, again from the simple circuits manual, with the multiplexed 4026B drivers and 2 separate 7 segment displays makes sense because each digit display has 7 input pins. I'm not sure how a single integrated unit 3 digits can be driven with only 12 pins??? And I can't see how a multiplexed system can be connected to only 12 pins. This is what led me to wonder if there was some internal controller built into the 3 digit display to allow a single external controller. I hope that makes sense. I tried searching for how they work but couldn't find any literature. I really would like to know.

And thank you Marks I'll definitely have a look at the project Marks cited. I only have 08M2's at the moment but I have found a quite decently priced supplier in Australia.

Thank you all.
 
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SteveT

Senior Member
@rextal sounds like you have a 3 digit common cathode display - yes?

1 cathode per digit, 7 (8 with decimal point) anodes in total. The anodes for each digit are joined together internally. You multiplex them in such a way that each cathode is switched in turn very quickly so that it gives the impression of all digits being on at once.

IE put the data on port B for the 100's digit - pulse the cathode of that digit. data on port B for 10's digit - pulse the cathode.....etc

Pretty poor explanation I know. Have a search for Westaust55's tutorial on using 74595's (If I recall correctly). That explains a lot.

found it
http://www.picaxeforum.co.uk/showthread.php?9230-Using-74HC595-to-drive-8-LEDs&highlight=%2A595%2A

No it's not - wrong one
 
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nick12ab

Senior Member
rextal said:
So looking at the 3 digit unit with only 12 pins I couldn't see how you would multiplex 3 of the 4511B's to control each digit individually as it would require 21 input pins on the 3 digit display plus those for decimal and power, theoretically to me the 3 digit unit should have a minimum of 26.
Click to expand...
Because the display you are using requires multiplexing, if you want to use 4511s to drive them you will need a multiplexer IC that has 7 (or more) outputs and at least three sets of inputs that can be switched between to connect to the outputs.

It would be better to drive the display directly using the PICAXE. A shift register can be used to reduce the number of pins required
 
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rextal

New Member
SteveT You are correct. After a lot more reading this is indeed what it is. I had surmised the additional pins were toggle pins were for changing the state for one of the digits on thereby strobing each one consecutively and discretely one at a time and it's repeating that process very rapidly that fools us humans into believing all are actually lit at the same time. This I believe wouldn't require multiplexing, that would only be if you wanted each digit to be permanently illuminated.

All I was thinking the Picaxe would control the on off state of one of the 3 digits directly and the 4511 would just signal the digit that was currently active. Seeing that all three digits are connected in parallel and you are just strobing on at a time in a sequence the 4511 should to my mind is only ever sending a signal to one digit. It's up to the picaxe to control which one it is actually being strobed. And this is why I was asking if there was still only 1 of the 4511 (or other driver) required for the integrated displays. I suppose you could still multiplex them so that their output is synced with the strobing but that seems like you've got three chips to do the work of one, provided that one chip can operate fast enough.

Thus to my thinking the only issue would be if the picaxe could actually time/coordinate the events accurately and quickly enough, which from some further reading on other forums may be the issue because the lack of a system timer which I think is required for the accuracy http://home.exetel.com.au/blavery/blavery.com/robotics/mtask.htm

I also noticed a discussion somewhere (not on picaxe) about the use of a tristate approach of the outpins. So as well as the traditional On, Off also use floating state to increase useable output combinations effectively increasing pin capability. It struck me that a tristate approach would mathematically be suitable for a 3 digit display that relies on strobing.
 
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SAborn

Senior Member
Basically you send the same data to all 3 displays and just lite the display digit that is intended for the data sent.
I think its around 20 times a second the human eye sees a constant light and little flicker, so i doubt the picaxe is so slow it cannot write to a 3 digit display fast enough it wont be seen as a consistent 3 digit display. (well infact i know it can).

Seems like a perfect case of too much reading and no trial testing, and just expecting Mr Google providing the answerers.
 
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rextal

New Member
Thank you all once again for all your pointers and comments. I'm desperately trying to assimilate it.


I have to admit I do use Mr Google a to help increase my knowledge and try ascertain if my speculations are correct but as someone with very few parts to play with and no breadboard this has to be the case. I've only made one project so far. I also know firsthand how long I can spend like a bull at a gate on a lost cause before realising it is a lost cause. I have bought 3 separate 7 segment displays and 3 SIPO shift registers to do some experimenting with.

I like the idea of shift registers for my intended use (CD Macro Rail) in which I want to add a 3 digit display showing the remaining pictures to be taken. Since there are several second pauses to allow any vibration to settle before taking a photo it will only require refreshing the display every 3rd second or so. From that point of view I couldn't personally imagine the PICAXE speed being an issue. Though it might be if applied elsewhere, and that's worth keeping in mind.

That project uses an 08M2 and only pin free is the serial out so what I was hoping to do was make a separate module using another 08M2, shift registers and digits. In a way this would be like a really cut display module (ie Serial OLED module, which I incidentally do have one). A few of my friends have expressed interest in me building them one with a display, however the Serial OLED module is more than double the cost of all the other parts put together (I got elcheapo eBay steppers). I'm quite keen on modular units as they're easier to build and test. A lot of consumer electronics I've pulled apart have the display board separate so it's easy to locate and mount where you want it, which is another factor. And as a programmer modular hardware should mean modular code.

I could, and may yet, use a 14M or 18M picaxe in the future ones I build so I have more pins but the current one is a fully soldered and fully functional so I'm not keen to alter it, however adding another module is fine.

Ultimately I'd like the project to interface with my PC and if possible have it controlled by the remote shooting software called 'Helicon Remote'. I know Helicon can control some third party macro rails and in the past the developer has been very good responding to issues like this. Obviously then an onboard display is pointless.
 
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SAborn

Senior Member
Can i suggest you use a 18m2 or bigger pin out chip, and simply use a LCD dispay, its a hell of a lot easier than fluffing around with 7 seg displays.

For example a 1x8 LCD will be about the same size numbers as a 7 seg, but you have up to 8 digits and also including text.

About $7.00 off ebay, and can be run direct from the picaxe, no fluffing around with driver chips and multiplexing and/or ..........?

It will also use a lot less power than a 7 seg.
 
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rextal

New Member
Thanks SABorn, good advice. I did see these when I was looking around but wasn't 100% sure they could be driven without further chips. Having more digits would be useful too, it's why I bought the serial OLED module for use on my own macro rail. The project uses IR input from a TV remote and as a user I'm not exactly positive about what I entered. On boot it relies on the user entering 2 digits on the remote, which is the number of stepper motor steps to increment by between shots. A confirmation of this number would be ideal. The starting position and end position are recorded by setting a start point via a remote with the total steps being determined and the number of shots to take is based on total steps/user input step size being somewhere between 1 and up to 150. So 2 digits for initial input, a space as a separator and then three more digits is I think the basic requirement. At a bare minimum the number of remaining steps is what I was aiming to display.

So long as I know it's possible I'll figure it out, even if it takes a while. At this stage for me knowing what is possible is a big help.

I will still build the 3 x 7 segment display using the shift registers as it will prove to be a very good learning exercise. I do like how just in programming there are multiple ways to achieve one task.
 
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