Release with Digital Timer and Electromagnet

Ideas and instructions how you can make your own bondage toys.
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GeneralError
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Release with Digital Timer and Electromagnet

Post by GeneralError »

Hi, currently I'm working on a little new project. It is an electronic timer that controls an electromagnet. It is still a prototype but it already works quite good and the programming is finished.
The idea is to create a simple and easy to handle standalone solution. The timer can be adjusted between 1 sec and 100 hours (99:59:59). When it is started it just counts down. When it reaches zero, the electromagnet is switched off. The little magnet is strong enough to hold a key or someting similar. So the usage scenario is like the CD tray opener or the key frozen in an ice cube. The magnet with the key is positioned out of reach in such a way so that the key falls into reach when it is released.
For the hardware I used a development board that comes fully loaded with esp8266 microcontroller, OLED display, 5-way switch, 18650 battery holde and charging electronics. (Google: InnovateKing Oled-Esp-18650 ) Only the electromagnet is missing. I again used this little guy: https://www.wish.com/product/5b5cd464ff666512b9871a11
The prototype looks like this:
sbtimerHW800.jpg
I hope I find the time soon to design a 3d-printable nice box for this little gadget.
Cheers
General Error
rmcingle
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Re: Release with Digital Timer and Electromagnet

Post by rmcingle »

Do you know what the current draw is for the magnet? Or better yet, entire circuit?

What I think would be ideal is if everything was mounted in a neat little box that included rechargeable batteries. Then you could hang the entire box from the ceiling or other high place and eliminate the escape of simply pulling the plug on the box. Not sure how big of a battery you would need to keep the magnet going for an extended time.

I use a much larger electro-magnet as my release mechanism. It doesn't drop a key, it is the electro-magnet that is what is holding me in place. Generally involving a rope threaded through a ceiling hook or other sturdy object. The trick is to keep everything arranged so that I can't manage to reach the power cord and unplug the power supply.

It is also a real good idea to have a backup release. If it ends up being battery operated, the battery will eventually go dead and release. If you are using wall power, plug it into a lamp timer set for a longer time period.

Another concern that you should test and retest: it is common for electro-magnets to have a 'residual magnetism' that remains even after the current shuts off. After the key has been held by the magnet for a while the residual magnetism (both in the magnet and from the key) might be enough to hold the key indefinitely. If that is a problem then either add weight or use a piece of paper/cardboard between the key and the magnet to reduce the magnetic field.

R. Mc.
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Shannon SteelSlave
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Re: Release with Digital Timer and Electromagnet

Post by Shannon SteelSlave »

Want to employ your talents on a higher level here, rmcingle? Send me a PM, you might be able to help us.
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A Jedi uses bondage for knowledge and defense, never for attack.
I am so smart! I am so smart! S-M-R-T!....I, I mean S-M-A-R-T!
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swswl
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Re: Release with Digital Timer and Electromagnet

Post by swswl »

Further to rmcingle’s point about residual magnetism, I would also point out that solely relying on the battery to discharge as a safety mechanism is not without issues, as LiPo batteries do not like being over discharged. Could be dangerous if they throw a tantrum while you’re bound. You could use a protection mechanism to prevent this. They sell for dirt cheap. They will shut down the output if the voltage gets under a certain level.

I personally use LiFePO4 chemistry batteries, as they are much less likely to go haywire. They have a different nominal voltage though, so that has to be considered.

Cheers
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Shannon SteelSlave
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Re: Release with Digital Timer and Electromagnet

Post by Shannon SteelSlave »

You'll need a low voltage detection switch to turn it off when a Lipo's power falls to 50%. Might be some kind of diode, like a zener type. Lipos are severely damaged by allowing them to completely discharge. Keeping them fully charged when not in use is bad for them as well.
If you insist on using a Lipo, you should use a "Lipo bag". Those Lipos are no joke, they can catch fire and do a lot of damage while you're bound, to say the least.
Bondage is like a foreign film without subtitles. Only through sharing and practice can we hope to understand.
A Jedi uses bondage for knowledge and defense, never for attack.
I am so smart! I am so smart! S-M-R-T!....I, I mean S-M-A-R-T!
👠👠
swswl
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Re: Release with Digital Timer and Electromagnet

Post by swswl »

Shannon SteelSlave wrote:You'll need a low voltage detection switch to turn it off when a Lipo's power falls to 50%. Might be some kind of diode, like a zener type. Lipos are severely damaged by allowing them to completely discharge. Keeping them fully charged when not in use is bad for them as well.
If you insist on using a Lipo, you should use a "Lipo bag". Those Lipos are no joke, they can catch fire and do a lot of damage while you're bound, to say the least.
For over discharge protection, something like this might do:
https://www.aliexpress.com/item/33057915333.html

If you use more than one cell in series, you’ll want to look at different boards. They are typically named after the number of cells in series, i.e. 1S, 2S, 3S, etc.
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Re: Release with Digital Timer and Electromagnet

Post by rmcingle »

Yes, you need to be very careful when using the more exotic battery chemistry.

I would NOT recommend using just the battery capacity as the sole means of escape. If you have an intelligent battery charge/discharge controller that will shut the battery completely off when the charge drops below a certain point it might be predictable enough to be safe, but just running a dry cell or NiCad down to nothing could end up taking a really long time. As the voltage dropped the current would drop and the rate of discharge drop. Like the residual magnetism I mentioned before, even a very small current could continue to hold the key a very long time.

If you wanted to use one of the more efficient battery systems buy something that has the charge and discharge protection built in rather than just the raw cells. What might work great is one of the USB Charger packs. These are the batteries that are intended to be a means of recharging your phone. They typically have a micro-USB jack for charging the battery, and then a USB type A (the large, flat connector found on your computer) for connecting the charging cord of your phone. You can buy these in a wide range of sizes for relatively cheap. The charge/discharge protection will be built in.

If you want a really long time to run, buy one of those portable car jump starters. They typically have USB jacks for getting 5 volts and other ports for getting 12 volts and have a fairly significant battery inside.

R. Mc.
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Gregovic
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Re: Release with Digital Timer and Electromagnet

Post by Gregovic »

Small point of note, 18650 batteries are not LiPo. They are Li-Ion. While related the Li-ion chemistry is a lot safer. For added protection I would advocate using either protected cells that have the protection circuitry built into the individual cell, or use a pre-built battery system with this protrction built in. A battery for cordless tools would work well, can generally be bought all over the world and can provide more than enough power at (usually) 12.6 volts (3s), with 8.4 volts (2s) and 16.8 (4s) also available. The 18 volt packs are generally actually over 20 volts (max 21.2, 5s cell voltage, sometimes with some electronics to lower the output voltage and increase battery life). Or use a USB powerbank at 5v with whatever cell count and capacity you want.
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GeneralError
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Re: Release with Digital Timer and Electromagnet

Post by GeneralError »

sbtimerBack800.jpg
rmcingle wrote:..... What I think would be ideal is if everything was mounted in a neat little box that included rechargeable batteries. Then you could hang the entire box from the ceiling or other high place and eliminate the escape of simply pulling the plug on the box. Not sure how big of a battery you would need to keep the magnet going for an extended time.
....
Such a little box is exactly the plan. The development board is already equipped with a battery holder for 18650 cells. As Gregovic mentioned, these are Li-Ion based. So far I have not measured or tested out, how long a fully loaded cell can power the board plus the magnet. I guess only a few hours. Since the electromagnet gets pretty warm, it seems to consume a lot of energy. But the advantage is the inherent fail-saveness: Empty battery => key gets dropped
Here is a picture showing the back side with battery holder.
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BoundInKasugai
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Re: Release with Digital Timer and Electromagnet

Post by BoundInKasugai »

Very nice work!
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GeneralError
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Re: Release with Digital Timer and Electromagnet

Post by GeneralError »

Now I designed and printed a casing for my sb timer:
sbtimer_v4_running.jpg
It still not complete. The eyebolt does not fit and the recess for the display is too big and so on. But it is already usable.
Because I also want to gather some experiences with publishing stuff on github, I created a public repository and uploaded the project.
If someone wants to take a look: https://github.com/blacknax/sbtimer
Kinky cheers
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Riddle
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Re: Release with Digital Timer and Electromagnet

Post by Riddle »

Nice work.
Resident timer maker. :hi:
Let’s make timers together!
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Re: Release with Digital Timer and Electromagnet

Post by lj »

the 18650 battery has an inbuilt charger regulation circuit - this switches off the incoming charge voltage when the cell voltage reaches the relevant cut-off (IIRC 4.3v but I may be wrong) and also limits the maximum charging current. It also open-circuits the battery when the cell voltage drops to the safe minimum.

This is based on my own experience using these batteries in a commercial design - I simply have a "wall-wart" supply able to supply more than the battery charge voltage, albeit deliberately at a relatively low current as a short charge time is not critical. I wouldn't consider using LiPo batteries in a device used indoors, with restricted human intervention! I have seen the fire (self-oxygenating and sustaining) when they go off - fortunately outside.
be a switch, double the fun :-)
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Gregovic
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Re: Release with Digital Timer and Electromagnet

Post by Gregovic »

lj wrote:the 18650 battery has an inbuilt charger regulation circuit - this switches off the incoming charge voltage when the cell voltage reaches the relevant cut-off (IIRC 4.3v but I may be wrong) and also limits the maximum charging current. It also open-circuits the battery when the cell voltage drops to the safe minimum.

This is based on my own experience using these batteries in a commercial design - I simply have a "wall-wart" supply able to supply more than the battery charge voltage, albeit deliberately at a relatively low current as a short charge time is not critical. I wouldn't consider using LiPo batteries in a device used indoors, with restricted human intervention! I have seen the fire (self-oxygenating and sustaining) when they go off - fortunately outside.
I feel I have to post this warning and please excuse the all caps bold large font but the following is VERY important:
NOT ALL 18650 CELLS ARE PROTECTED WITH BUILT IN CELL PROTECTION CIRCUITRY

If you are going to use 18650 cells in a project, make sure you know which type of cell you have (protected or unprotected) and make sure that there is battery protection in the system somewhere. Either in the cell itself or in a separate board. Having 2 protection boards "stacked" is not ideal but not really a problem. Not having any protection is nor good idea.

Now, some manufacturers would have you believe unprotected cells are hand grenades waiting to go off, and while nasty things CAN happen, it's unlikely if you are careful with how you use them.

LJs method of charging works with protected cells but it is downright dangerous with unprotected cells (though I would normally advice against charging cells that way as the inbuilt circuitry isn't really design to dissipate all that much power at the end of charging cycle).

I have some unprotected cells around for certain projects where there is BMS circuitry externally and I actually keep those in a LiPo protection bag.
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CD Tammy
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Re: Release with Digital Timer and Electromagnet

Post by CD Tammy »

I use a door magnet and a WiFi plug. In the Kasa app, I can set a timer or time to release. If the power goes out, the lock will release.
03D56672-F4FA-4510-AC04-6764DFF3518C.jpeg
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