Safebox design

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#1
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Hi,

I want to design an electronic safebox with 500 boxes or more. There is a central RFID reader in which every customer is given a tag. When the tag is approached to the reader, the relevant box will open. I thought I could use a reader for each box but this will become costly.
RS485 was another choice due to noise immunity and long range but it supports maximum 320 nodes:
http://www.ti.com/lsds/ti/interface/rs-485-products.page
In this scenario, a single reader is installed and all other locks are controlled via this protocol.
Wireless communication(Zigbee?) was another option but I am really afraid of using it due to high cost and complexity.
I2c again rejected as it supports 128 nodes. (AFAIK)
LAN connection? using a Wiznet W5100 and a a single attiny13a? Is it cheap and practical?

What do you think is the best option?

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A strong crowbar.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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Thoughts on Instanbulkart? (note also the Akbil that's apparently being replaced) (Wikipedia, Instanbul public transit)

"Dare to be naïve." - Buckminster Fuller

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Torby wrote:
A strong crowbar.

Sorry for my poor English.Did you mean this?
http://en.wikipedia.org/wiki/Crowbar_%28tool%29

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Does the communication between the master with the reader and the individual boxes have to be two way? If only one way, you can make an RS422 "repeater" to isolate sections and allow 200+ nodes per section. BTW, RS422 and RS485 differ (mostly) in that 422 has a single data originator and many listeners while 485 allows any device to be a master.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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Perhaps I'm missing something, but why not just have two RS4xx buses. Units 1 - 250 are on one bus, 250 - 500 are on the second bus.

I would expect each box to acknowledge a command being sent to it, and to also send back its status, (open or closed). LED array or PC Display with 500 nodes showing which are opened, which are closed.

JC

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Two busses would also work but that takes two UARTS.

I have built systems for MANY nodes in a loop with RS422. Output of one goes to input of next. Output of last goes into input of master. Use message ID numbers to mark ack messages and control messages. Any message addressed to device N stops at N; any other passes through. Master does not forward anything received. Works quite well and no segment of the loop has more than one receiver.

Jim

 

Until Black Lives Matter, we do not have "All Lives Matter"!

 

 

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If cost is that much of a concern, does each individual box need its own brain? Presumably you'd need a solenoid to open the latch, a switch to detect door position,and maybe an LED or two per box. You could assemble the boxes into units of, say, five boxes each-then you only have to worry about talking to 100 nodes instead of 500.

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Yup. That's it.

If you don't know my whole story, keep your mouth shut.

If you know my whole story, you're an accomplice. Keep your mouth shut. 

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I don't think a single reader for 500 boxes is a good design decision. Imagine 500 people at the airport wanting to get to the reader at the same time... or even 50 people. Riot!

Ross McKenzie ValuSoft Melbourne Australia

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Or imagine a single RFID Reader failure... 500 locked boxes without access.

JC

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valusoft wrote:
I don't think a single reader for 500 boxes is a good design decision. Imagine 500 people at the airport wanting to get to the reader at the same time... or even 50 people. Riot!

Indeed right! I had not considered that!
What about a reader for each 50 boxes?

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ka7ehk wrote:
Two busses would also work but that takes two UARTS.

I have built systems for MANY nodes in a loop with RS422. Output of one goes to input of next. Output of last goes into input of master. Use message ID numbers to mark ack messages and control messages. Any message addressed to device N stops at N; any other passes through. Master does not forward anything received. Works quite well and no segment of the loop has more than one receiver.

Jim


If I use RS485, can I send the status of a lock to the central reader? like status of each node goes to next node and so on til reaches the central reader and then I can display it?
As of RS422, if the nodes are only listeners, then sending ack and status is not possible. Am I right?

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In the RS485 hardware layer, all slaves are listening across the lines at the same time. The way the slaves respond is determined by your software. Ordinarily, they do not pass the message along as you have described. If they did it that way, if one died and stopped passing the messages, all of the slaves past it would be out of contact. Bad software design.

The software layer should cause each slave to "listen" for its identity number and accept the command following that ID. All the other slaves should ignore the command because it is not its ID.

You can allow each slave to respond to its command with either an ACK or perhaps the safelock status. You define in software how it is to operate. The master will wait for this response after it has sent the command. The master must have a wait time defined to allow for a slave that fails to respond in a reasonable time.

You can also assign a group ID so that the one command sent to the group causes every slave to do that command, for example "reset".

Hope that helps you.

...and no I think 50 per reader is still too many. Perhaps you could have one reader per set of safes. If they are installed like filing cabinets next to each other, perhaps 3 safes per cabinet and 4 cabinets per reader... so one reader per 12 safes. Can you show us a picture of your safe?

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia

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Quote:

What about a reader for each 50 boxes?

Only you know the frequency with with people will arrive to open their boxes. Only you know the budget of your project.

Also consider this: If these boxes are in a crowded area, you really want any box to be within a few feet of its reader.

Imagine you where standing at a wall with boxes, five metres to each side of the central reader. There are hundreds of people in the vincinity, and five or ten of them are standing within a meter of the row of boxes. Your box is at one of the ends - i.e. you have to walk five meters to it after putting the tag to the RFID reader. At least three of the people are within two meters of your box when it opens. Non of them is you. Would you like to use such a system? What would you dare place in the box under these circumstances?

As so often there is much more to a good system than the purely tehnical. In almost all cases you have to take human nature into consideration when designing a system.

As of January 15, 2018, Site fix-up work has begun! Now do your part and report any bugs or deficiencies here

No guarantees, but if we don't report problems they won't get much of  a chance to be fixed! Details/discussions at link given just above.

 

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valusoft wrote:
In the RS485 hardware layer, all slaves are listening across the lines at the same time. The way the slaves respond is determined by your software. Ordinarily, they do not pass the message along as you have described. If they did it that way, if one died and stopped passing the messages, all of the slaves past it would be out of contact. Bad software design.

The software layer should cause each slave to "listen" for its identity number and accept the command following that ID. All the other slaves should ignore the command because it is not its ID.

You can allow each slave to respond to its command with either an ACK or perhaps the safelock status. You define in software how it is to operate. The master will wait for this response after it has sent the command. The master must have a wait time defined to allow for a slave that fails to respond in a reasonable time.

You can also assign a group ID so that the one command sent to the group causes every slave to do that command, for example "reset".

Hope that helps you.

...and no I think 50 per reader is still too many. Perhaps you could have one reader per set of safes. If they are installed like filing cabinets next to each other, perhaps 3 safes per cabinet and 4 cabinets per reader... so one reader per 12 safes. Can you show us a picture of your safe?

Cheers,

Ross


Ross Thank you for your great explanation. Well, I do not have any picture of my safe though it is of the ones used for temporary storage used in airport, bus terminals, etc. I will post a picture as soon as I get the cabinets. Can I implement what you mentioned with RS422? BTW, what chip do you recommend for this communication?

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valusoft wrote:
In the RS485 hardware layer, all slaves are listening across the lines at the same time. The way the slaves respond is determined by your software. Ordinarily, they do not pass the message along as you have described. If they did it that way, if one died and stopped passing the messages, all of the slaves past it would be out of contact. Bad software design.

The software layer should cause each slave to "listen" for its identity number and accept the command following that ID. All the other slaves should ignore the command because it is not its ID.

You can allow each slave to respond to its command with either an ACK or perhaps the safelock status. You define in software how it is to operate. The master will wait for this response after it has sent the command. The master must have a wait time defined to allow for a slave that fails to respond in a reasonable time.

You can also assign a group ID so that the one command sent to the group causes every slave to do that command, for example "reset".

Hope that helps you.

...and no I think 50 per reader is still too many. Perhaps you could have one reader per set of safes. If they are installed like filing cabinets next to each other, perhaps 3 safes per cabinet and 4 cabinets per reader... so one reader per 12 safes. Can you show us a picture of your safe?

Cheers,

Ross


Ross Thank you for your great explanation. Well, I do not have any picture of my safe though it is of the ones used for temporary storage used in airport, bus terminals, etc. I will post a picture as soon as I get the cabinets. Can I implement what you mentioned with RS422? BTW, what chip do you recommend for this communication?

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JohanEkdahl wrote:
Quote:

What about a reader for each 50 boxes?

Only you know the frequency with with people will arrive to open their boxes. Only you know the budget of your project.

Also consider this: If these boxes are in a crowded area, you really want any box to be within a few feet of its reader.

Imagine you where standing at a wall with boxes, five metres to each side of the central reader. There are hundreds of people in the vincinity, and five or ten of them are standing within a meter of the row of boxes. Your box is at one of the ends - i.e. you have to walk five meters to it after putting the tag to the RFID reader. At least three of the people are within two meters of your box when it opens. Non of them is you. Would you like to use such a system? What would you dare place in the box under these circumstances?

As so often there is much more to a good system than the purely tehnical. In almost all cases you have to take human nature into consideration when designing a system.


Nice hint. I had not considered that. That comes from a professional engineer. I am still at its technical implementation.

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ereihani wrote:
BTW, what chip do you recommend for this communication?

There are 3 chips that I am aware of that can do what you need, but I do not know about their availability in Iran.

SN75176
MAX485
LTC485

Could I also suggest that you investigate using the SNAP software protocol ( http://www.hth.com/snap/ ) running on the RS485 hardware layer. There are plenty of examples.

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia

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valusoft wrote:
ereihani wrote:
BTW, what chip do you recommend for this communication?

There are 3 chips that I am aware of that can do what you need, but I do not know about their availability in Iran.

SN75176
MAX485
LTC485

Could I also suggest that you investigate using the SNAP software protocol ( http://www.hth.com/snap/ ) running on the RS485 hardware layer. There are plenty of examples.

Cheers,

Ross


SN75176 is available. I would study the examples in the above website. Thank you for your help.

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Is designing an RFID reader hard and costly for each lock? I saw some reader chips like ATA6285 or HITAG reader with less than 2 USD for each piece? AFIK, the RF design part is somehow complicated.

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Could I suggest that you watch this youtube video from Elektor. The man on the right hand side is Martin Ossmann who is also one of the AVRFreaks (Ossi). He discusses using an avr to make an RFID reader/writer.

http://www.youtube.com/watch?v=n...

Cheers,

Ross

Ross McKenzie ValuSoft Melbourne Australia