Need design help

[Gopher 77]

It's been a long time since I have designed even simple circuits so I could use some help. I need a control board to power 4 electromagnets and reverse polarity when a signal is received from a momentary switch. its in a 12 VDC system and amperages should be pretty low. I'm hoping to get off the shelf (like radio shack) type components to build the board. I do have a strong (military) background in electronics, but my job was mainly swaptronics to keep systems up and running. So I can build the board, I just need some design help. I have attached a block diagram of how the system needs to work. Thanks for any assistance.

Cheers,
Dave

 

[Alec_t]

Welcome to EP!
Can you clarify this: "The master control when first turned on immediately changes polarity after 5 sec delay reverses polarity"?
A timing diagram would help.

 

[AnalogKid]

In round numbers, here is how this goes. If all 4 magnets are always switched together, then you need only one reversible power stage. That is called an H-bridge, or full H-bridge driver. With a single power system, like +12 V only, it can place almost 12 V across the coils in either direction. Depending on the total current involved, you probably can use a single-chip H driver rather than grow one from scratch. OTOH, this can be done with two SPDT relays.

The two switches go to the two inputs of a set-reset flipflop. The first press of either switch causes the ff to change state. Successive presses of the same button do nothing. First press of the other button changes state. Etc. FF outputs drive the H-bridge or relays.

ak

 

[Gopher 77]

Alec,
Thank you for such a quick reply. Timing is mostly event driven, the only place it is time driven is at the initial turn on. I didn't define the master control very well. It is a control voltage (can be any voltage and amperage) to turn the whole system on and off. hen the voltage is present the system operates, when it is not it does not. Since there is no way to know which state the system was last in (state 1 or state 2 as defined by the momentary control switches) the system need to power up operate in which ever state it was last in (which it will do by default) and then switch state so that it is guaranteed to cycle through both states. Then enable the state switches and they will operate on normal function from there. Am I making any sense?
Thanks,
Dave

 

[Gopher 77]

AK,
That's exactly the type of operation I need. I will take a look at the OTOH!
Thanks,
Dave

 

[AnalogKid]

Once the unit is running, is there any time when the magnets are off, or is it always one polarity or the other?

ak

 

[Gopher 77]

Once the unit is running the magnets are always on. If the unit is "turned off" then it would restart from an unknown condition. This is something very simple I am making to illustrate induction for a class I teach.