Transmitter & receiver modules

[Natalie Wilkie]

Hi All,

I intend to have a picaxe 28x1/40x1 controlling a 5 digit 7 segment led counter, it counts in 1 second increments using a DS1307 ic. The leds are driven by decoder/latch drivers.

I would like to be able to control (start, pause, reset, resume etc) it remotely, say up to 60 odd metres away and maybe through a thin dividing wall. I don’t want to use an infrared sensor I was more thinking of using an RF transmitter & receiver 433Mhz modules something like this: http://www.computronics.com.au/module/txrxpair/


From what I have read when using the serin and serout commands no other commands are executed (is this right) and this would interrupt my counting or/and slow things down and I need responses to happen quickly and reliably.

I intend to have a 08M controlling the transmitter and at the other end another 08M controlling the receiver and then this 08M receiving the data feed inputs of the 28x1/40x1.

My question is:
Is this over the top, will it work, will it ensure that the response from the transmitter will happen more quickly as this is all that the receiver 08M has to do?

Constructive criticism is most welcome.

Nat

 

[premelec]

I think this boils down to how fast you can get the data from the DS1307 and I don't know the answer... in short if you can read the time fast then you have time, within a second, to send the data out via 433MHz link though there will be some skew in time delay to send and receive said data... take a look at DS1307 data sheet and other posts on this forum... good luck with it...

OK I just took a look at the DS1307- do you only need 1 second marks? It appears this pretty complicated RTC will do that however a much simpler source is a battery "quartz clock" unit which puts out pulses to move the hands... and doesn't require any special setup instuctions and is backed up by it's own internal 1.4v battery... The DS1307 1Hz square wave output would also work and you'd have time to do some processing and data sending and receiving within the 1 second interval...

 

[manuka]

I'd also say that such a project has several "modules" & that these should be addressed in their own right. Hence suggest you individually tame 7-seg driving (which the new 20M is well suited for),clock control/setting, power supplies & 434 wireless issues- rather than do the whole lot at once. What are you intending this for? Where are you? Budget? Skills? Resources? Experience? Time frame? Help allowed? Stan

 

[lbenson]

With the 28X1 you can use background receive (look up hsersetup) so you wouldn't need to use an 08M on that end to prevent your code from hanging. The 28X1 can check for input at its convenience.

 

[BCJKiwi]

As the DS1307 does not have a seconds output via i2c, the seconds update cannot be read from the DS1307.

Maybe the answer is to use the setint command to monitor the SQW/OUT signal which can be set for 1 Hz. This provides the seconds data. The setint at 1 sec intervals would interrupt the serial if taking place at the same time.

Depending on what the communications involved, there may be insufficient time to process the interrupt, update the displays, and handle the serial commands.

However, if you up the clock speed to 16MHz on the 28X1 and use an i2c driver chip for the 7 seg displays then there should be plenty of time to do the rest - depending of course on what 'the rest' actually is!).
The i2c bus can run faster if a newer (and faster i2c bus) RTC chip is used such as the DS1337 or DS1338 which will improve cycle time.

The 28X1 also has a timeout on hserin which should simplify management and error recovery of the serial as a serial failure will not hang the 28X1.

 

[Natalie Wilkie]

I am using a proven circuit that I designed constructed last year and I want to build another one with bigger leds (4” – 8”) so it is easier to see from a distance and add a few more features – like remote control. The ds1307 I am using is only for the 1 hz sq wave output at this stage for an accurate 1 second increment but would like to use the features of the rtc to output the time when it’s not being used as a timer. A loop is used to search for the high and low of the 1 hz output. From memory I was going to use the setint but I had it wired to the wrong leg that wasn’t compatible.

I must have a look at the hsersetup and hserin command to try and work out how it works.

To Stan, I have no time restraints and no budget as long as it’s not too expensive and skills, well I’m still learning, I did my advanced cert about 10 years ago but don’t work in the electronics field. Australia.

To BCJKiwi what i2c driver chip for the 7 seg displays are you thinking of?

Thanks for comments so far

 

[BCJKiwi]

There is a raft of different chips, some more complex than others and everyone seems to have their favorites.

Many here favour the shift registers but they take time to step through as they need to pulsed for every segment of the 5 X 7.

My preference is to send the info via i2c and tell the chip what you want to do in a single output via i2c.

Current loadings need to be considered as driving 5 x 7seg LEDs - specially larger ones which have multiple LEDs per segment - takes some current.

There are two approaches to this - straight forward I/O expanders, or specialised LED driver chips.

Have only used the I/O expander approach but the projects are not clocks or counters - have different data sources on different outputs so deal with them one at a time. For this I use MCP23017s but you could use 1 x mcp23008 for each 7 seg, that way you will have plenty of current but if you don't need them so bright then you could use 2 mcp23017s and 1 23008.

For the specialised chip approach you could look at something like the MAX6958 (36 discrete LEDs = 5 x 7seg + 1 x DP), MAX7219 (8 x 7Seg).
There plenty of 4 digit (28LED) units but not many that handle 5 digits (35 + DP) in a single chip.

I'm sure others will suggest further alternatives.

 

[Natalie Wilkie]

Another question if I may.

Does the quality/reliability of these cheaper transmitter/receiver module differ to the slightly more expensive ones?

Something like these http://www.radiometrix.co.uk/dsheets/tx2rx2.pdf not sure how much (I'm sure they are more expensive) or these cheap ones http://www.computronics.com.au/module/txrxpair/ or even the ones you can get at Jaycar.

In this case do you get what you pay for, or are you just wasting your money??

Thanks again
Nat

 

[moxhamj]

The radio link problem still hasn't quite been solved! Well, technically, it has with really expensive gear but lots of people don't have a few thousand dollars spare.

Radiometrix keep their prices secret so no-one really knows how they compare.

Many people on the forum have been doing range tests with various modules. The latest ones to be tested are from Hope.

To some extent, the milliamps consumed gives an indication of range. Ones that use 5mA at 5V won't go as far as ones that use 100mA at 12V. And receiver sensitivity changes the range as well.

And if you go too high with the power (1/2 a watt) the RF gets back into the picaxe and does strange things to it.

Then there is the issue of interference to other people. Some of the higher power modules may be illegal to use. But that may not matter if you are in the middle of the Simpson desert.

I got 500 metres with this setup http://www.instructables.com/id/Build-a-500-metre-radio-data-link-for-under-40./

But I think you don't need that sort of range, and these higher power modules need the antenna moved away from the picaxe so you have to build an antenna. A compromise might be to use the same receiver as the one in that instructable, and use the transmitter on the last page (page 7). That combination is about 80 metres with simple dipoles (ie a wire soldered on the board for the antenna, and another wire of the same length soldered to the earth connection.

Do you have trees etc in the way?

 

[krypton_john]

BJCKiwi, are there any NZ suppliers for the MAX i2c chips?

 

[Natalie Wilkie]

Distance isn't a problem I don't think, I'm only looking at around 50 to 60 metres max. The only obstacle I might encounter is a thin wall (plasterboard).

Also how quickly do these transmitters/receivers respond after pushing the button at the transmitter end and getting a response at the receivers end?? Are we looking at milliseconds or seconds and are they reliable??

Thanks

 

[BCJKiwi]

@Krypton_John

The current MAXIM NZ Distributors are Powertech;
http://www.powertech.co.nz/
Don't know if they have these or not but Maxim will supply samples to NZ via Powertech.

Most of the other things I need I tend to get from Futurlec as they only charge regular postage rates for shipping - takes about a week to arrive. They don't seem to have the 69xx series but do have the 7219 (SPI) and quite a few others;
http://www.futurlec.com/ICMaxim.shtml
It is interesting to note that the 69xx and 72xx series led Drivers actally charlieplexed internally!

Trust this helps

Have been following the charlieplexing and shift register approaches in some of the other threads but have not tried those approaches yet.

 

[moxhamj]

Milliseconds. If you are just turning something on you might send UUUABCn where UUU stabilises the Rx (01010101), ABC is a unique header for serin, and n is a number. Time per character is about 1/10th the baud rate, so at 2400 baud that will be 1/240th of a second per character. The code goes straight on once serin has executed.

I'd maybe look at an 08 or 08M waiting for the data, then it could raise a pin high to say it has some data, and then the main picaxe 28X or whatever checks that pin, and puts another pin high and the 08M sends the data. That way there is no delay. Or use an interrupt to the 28X from the 08M.

Do it in stages. Get the display working. Get the clock working. Get the controller working with wires. Then replace the wires with radio links. So the radio bit might be the last bit to do, but yes, it can be done.

 

[MPep]

@Krypton:
If you request a sample from the MAXIM website, they will be delivered via PowerTech to you. They are now the sole distributor for MAXIM stuff.

Or you can try RS Components, Farnell, etc.

Mark.

 

[krypton_john]

Thanks for the pointer guys. I'm amazed in this day and age that you can get samples. Hopefully this won't be abused and will long continue!

 

[BCJKiwi]

@Mpep,
Have you compared prices from RS and Farnell with Futurlec? - I only use them as a last resort.

 

[krypton_john]

Well, I looked at Futurlec after you pointed me there, BJCK, and am amazed. Not only are they cheap, but they have a chip for everything!

 

[MPep]

@BCJKiwi,

I am very well aware of the pricing that RS and Farnell have. But if you cannot find another way of getting parts, what option do you have?

Only just prior to logging in, was I browsing Futurlec. They have some very interesting items on their books, don't they.

I was only offering alternatives. I highly recommend the free sample service, from Maxim and others.
They are meant for prototyping services, and after proving successful, you then order 2 - 10 thousand of whatever.

But for the one or two that we generally require, why not?!

I know a guy who orders samples from Microchip. He never runs out!

Mark.

 

[BCJKiwi]

Yes, sourcing into NZ is a bit of a pain.

I searched long and hard and found most suppliers charge prohibitive freight rates.

So my current order of supplier preference is;
PHAnderson for PICAXE and anything else he has including LCDs etc, Price and freight can't be beat - Picaxe chips land for < half the local price! - also has 5mm Leds with built in 330R in bags at a very good rate
Sicom - but only if I know exactly what they are offering. They typically have no datasheets or even pictures for their products. Arvind is quite helpful - if he answers at all.
Futurlec - if they have it,
Jaycar - but depends on the price/urgency - trade card helps for orders over $25 after discount,
RS (no freight costs - I can pick up as their Auckland branch is not too far away) - get just about anything from just about anywhere,
Farnell ($10 minimum freight on top of the already high prices).

Surplustronics are OK but their range is very sketchy and the pricing variable.
Have also purchased some items from;
RobotstoreHK (compass CMPS03) - best price/delivery I could find, prompt no hassles.
Dimension Engineering.com (Accelerometer)
Glyn are the local distributors for VDrive2 (I have one of these I don't need if any one is interested - PM me),
Dontronics (Australia) - a selective range of product and reasonable freight rates
uAlfat direct from GHIElectronics USA

Please add to the list for NZ if you have other suggestions.

 

[moxhamj]

I've just completed testing on the HopeRF modules (see recent posting on another thread) and these gave 250 metres. Plus they are transceivers, so you can send some data, then the other unit can send it back. That way, you can be sure the data is getting there with 100% reliability. So far I believe they may be the cheapest module in terms of $ per 100 metres.

 

[MPep]

Hi BCJKiwi,

An excellent list of suppliers. Like you, I believe sourcing from overseas is just about the only option in some instances.

Sicom I have found quite good. Arvind is not the only one. All 3 appear to have a good general knowledge of things electronic.
They are local to me, so no shipping costs for me

Mind you, I only buy stuff that I know works/does what is required.
Researching parts and data-sheets are a MUST for all inexperienced and experienced users alike. Then if it doesn't work, you can only look back at yourself and say, " bugger, should have thought of that ......." Fill in as required!

I have found in the past that whilst looking at a manufacturer's website and in particular Application Notes, reference is made to another component. The other component may be more applicable to the project at hand.
And you have learnt alot along the way, even if you never use it.

Mark.