My New Project

[eMagic259]

Hi folks I would be grateful for some help......

I am an amateur magician with a keen interest in electronics and now that I am retired, I have been trying to keep my brain active and my mind off the virus by making some electronic magic effects for my own use / pleasure (NOT FOR SALE).

However, the current challenge I have given myself is proving to be…well, a challenge…the old grey matter isn’t what it was and I was wondering if someone out there could and have the time to help me?

Here is my idea and what I am trying to achieve…….

I placed 8 small objects in a compartment box with a lid (2 rows of 4). While my back is turned the spectator / helper (normally my wife) removes a number of objects (any number) and I instantly know which objects have been removed. This is achieved by a 2 by 4 LED display on a remote receiver which shows the corresponding position of the objects in the box.

Currently I can get it to work (after a fashion)…..

Transmitter circuit – I am using 8 Hall Effect sensors hidden in the bottom of the box and there is a magnet hidden on the underside of each object. The 8 sensor outputs are fed to individual 555 timing circuits and then through inverters to the 01 to 07 address inputs of a HT12E Encoder. The encoder is connected to a 433Mhz Superheterodyne 3400 RF Transmitter for data transmission. The timing circuit allows for a selected object to be replaced and another chosen before the end of the trigger cycle...I have this set to 12 seconds.

Receiver circuit – the 433Mhz Superheterodyne 3400 RF Receiver data line is connected to 8 x HT12F Decoders, which in turn light there corresponding LEDs through transistor switching circuits.

The problem with the above circuit is that when an object is removed its corresponding LED only lights for a few seconds (set by the 555 timing circuit), and during the period that the LED is lit no other object can be removed or that data will be lost. Also, I start with all LEDs off and end with them all off, so I have got to keep a mental note of which LEDs were lit during the removal process.

What I really want to achieve is the following, but without using a microprocessor (if possible)….

With all the objects in the box I get 8 LEDs lit on the receiver and as each object is removed the corresponding LED is extinguished……i.e. if 3 objects are removed then 3 LEDs are extinguished corresponding to the position of the objects removed from the box (the remaining 5 LEDs remain lit).

I have looked at other options…..logic circuits, different encoder / decoders, latching circuits, etc, but it’s encoding / decoding the multiple input / selection requirements (decimal to binary to decimal) that is giving me the problem / headache.

Any help would be very much appreciated.

Stay safe and well!

 

[Ian Rogers]

without using a microprocessor (if possible)….

For any particular reason?? It does cut the circuit to very few IC's I thought the logic on the HT12F output would constantly update thus albiet a slight flicker the same data would present itself each read.. Or does the box lid initiate a transmission?

 

[Nigel Goodwin]

This is yet another example of people trying to use the HTxx chips for something they aren't designed to do - people see what's it's described as, but don't really understand what it means.

Don't mess about with HTxx remote control chips, or 555's etc. - use a microcontroller - it's ideal for this purpose, and reduces the size and complexity of your design massively.

 

[eMagic259]

Hi Ian and Nigel,
Many thanks for responding. The main reason I didn't want to go down the microprocessor route is because I have very limited knowledge in this area......a completely new learning curve for me (hardware / software / programming). However, I do understand and I think in my mind I knew that one day that bridge would need to be crossed.
If you can give me any pointers to get started then that would be very much appreciated.
BTW, the transmission is initiated by the removal of an object as sensed by the Hall Effects IC's, not the box lid.

 

[Nigel Goodwin]

Hi Ian and Nigel,
Many thanks for responding. The main reason I didn't want to go down the microprocessor route is because I have very limited knowledge in this area......a completely new learning curve for me (hardware / software / programming). However, I do understand and I think in my mind I knew that one day that bridge would need to be crossed.
If you can give me any pointers to get started then that would be very much appreciated.
BTW, the transmission is initiated by the removal of an object as sensed by the Hall Effects IC's, not the box lid.

I would suggest you get an Arduino to play with, if you buy it as a kit you get various sensors and components to play with as well.

Now an Arduino is a development system, but you can get much smaller Arduino Nanos and Minis to use for a finished project, or jumove to just a bare chip.

The Arduino has an incredible amount of support, and libraries are available for pretty well anything you need, such as in your case direct support for your cheap RF modules, no silly decoder chips needed.

 

[eMagic259]

Hi Nigel,
Many thanks for the info and recommendations......all greatly appreciated.
Off to start the ball rolling.

 

[Pommie]

I agree with Nigel, start down that road of Arduino. When you get stuck, just ask.

Mike.

 

[eMagic259]

Thanks, Mike.

 

[dr pepper]

If I get it correct could you do away with the electronics and connect the leds direct to the hall sensors, then with the object in place the led lights, no object in place no light.

 

[rjenkinsgb]

It could be done with a pair of UARTS, 8 bit parallel data in from the switches, serial via the radio modules and back to parallel for display. It would not need all that much extra logic beyond the UART and clock oscillator at each end.

That would give a real-time mimic of the hall sensors on or off.

UARTS are getting a bit scarce, but there are still places selling them on ebay - eg.

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DigChip IC database

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[eMagic259]

Hi dr pepper,

Many thanks for your input.

Yes, in its simplest form it could be done like that. The LEDs would need to be subtly concealed in the box and controlled so that only I could see them when required. I have used this method in other effects, and it works well.

However, the challenge I gave myself this time was to have the selection information transmitted to a remote receiver / location.....i.e. out of view and to reduce the risk of any potential detection by the spectator (helper).

 

[Pommie]

Sending rs232 data via radio without manchester encoding is very unreliable.

Mike.

 

[Nigel Goodwin]

Sending rs232 data via radio without manchester encoding is very unreliable.

And no need to with the Arduino, as there's a library for using the cheap radio modules reliably, and there's even a similar PIC version available.

 

[Pommie]

And no need to with the Arduino, as there's a library for using the cheap radio modules reliably, and there's even a similar PIC version available.

It was suggested above to omit the arduino and send the switch outputs as an RS232 stream.

Mike.

 

[eMagic259]

Hi rjenkinsgb,

Many thanks for your suggestion / recommendation.

I have no knowledge of the UART and apart from the datasheet, I can't find any additional info or practical application data.

For now I think I will continue to explore the Arduino / microcontroller route as there is a vast amount of support in this area.

 

[Pommie]

Thinking "out the box". If you use an esp8266 based board (wemos mini) then it can be setup as an access point and your phone could connect whilst in your pocket. It could then vibrate a code to convey the answer. Not as hard as it sounds.

Mike.
Edit, anyone know if you can use the vibrator via javascript?

 

[dr pepper]

I think I get it now.
You can do it with sound, Dtmf tones, I cant remember the number of the transmitter chip, but I seem to recall the rx is a holtek 8870, you could use a wire to send the sound, or a couple of those cheap modules that have analogue.

 

[eMagic259]

Hi Mike,

Many thanks......I can see how the vibration indication would work if a single object was removed from the box, but in the scenario I have described above the spectator has the option of removing multiple objects. In this case you really need a visual indication to keep track of what is going on.

The electronics for removing 1 to 4 objects and having the information transmitted to a remote location is relatively simple....however, more than 4 and that's when the fun begins.

 

[Pommie]

Two quick beats to indicate start and then n long or short beats to indicate present or not. There are many ways to convey information. If you hold the box then a magnetic ring could activate another sensor to vibrate the info to you. No remote anything required.

Mike.

 

[Pommie]

Remember the early phone tone when a text was received, beep beep beep, beeeeeep beeeep, beep beep beep. Morse code for sms and nobody (actually a few people here) knew.

Mike.