I am looking to make an electrically actuated shutter for a pin hole camera. Having looked at commercially available solenoid they are generally larger than I would.like so I am thinking of making my own.

The question I have is what is the best core diameter, wire size and number of turns to get a small but efficient electromagnet? I'll be driving it from a 555.

 

Hi sirch, what sort of size is acceptable for you?

 

What shutter speeds are you hoping to achieve? Solenoids can be quite sluggish.

 

hi sirch,
This PDF covers miniature solenoid designs.
E

 

Relays are a good source for coils and armatures.

 

Thanks all, size wise I'm hoping for something of the order of 8mm diameter or less by 20 to 25mm long for the coil.

Shutter speeds are in the 0.5s to 3s range.

Thanks for the pdf links

Good idea about harvesting a coil from a relay, I'll look into that.

 

Would this be too big?
https://www.aliexpress.com/item/6pc...lgo_pvid=6833fabd-dc63-4d88-bf6a-2a4bb978aa01

 

Good idea about harvesting a coil from a relay, I'll look into that.

You should while doing that, look to see if the whole actuator of the relay can be incorporated. By that I mean the parts that move the contact points, just add a linkage from that to your shutter.

 

Perhaps use the tiny vibration motor from a phone? Wouldn't need much modification.

 

RE: ""what is the best core diameter, wire size and number of turns""
If any You choose to wind it DIY, here are the core thumbrules:
1) any steel core (except samarium and neodimium) may achieve a maximum maximorum 10 kg/cm2 of cross section at 1,6 Teslas. Thus, better operate with half of this.
2) any magnet have worst case scenario when air gap is maximal, thus at the very start of sliding the core inward. To calc it, may use the formula n(turns)*i(Amps)=B(Teslas)*[(hcore/(mju zero/mju relat))+hair/mju zero)]. Thus, for the case of steel and air n*i/B=[h ferrum/(4400)+h air]/12.6E-7. Respectively the force F(Newtons)=B^2*A(sq.meters)/2/mju zero/mju relat
If any would will to feed it by DC, then i is governed just by Ohmic resistance of coil wire, thus calc the length and apply the resistor maker formula.
If any would apply the AC, then damping a vibrations may demand an enormous much job, but i then is governed by impedance.

 

Would this be too big?
https://www.aliexpress.com/item/6pc...lgo_pvid=6833fabd-dc63-4d88-bf6a-2a4bb978aa01

Thanks, I know that is close to what I specified above but it just "feels" a bit over-kill, the shutter will just be a sliding blade weighing a couple of grams.

You should while doing that, look to see if the whole actuator of the relay can be incorporated. By that I mean the parts that move the contact points, just add a linkage from that to your shutter.

I was considering that but, being determined to make life difficult for myself, the pinhole camera is a tin can, so the inside where I want to mount the shutter is not flat. Pulling the shutter vertically upwards is easy enough but life could get complex with linkages etc.

 

Hi sirch, one other thing occurred to me, you could look at using a similar arrangement to a hard disc drive head mechanism:
https://www.featurepics.com/StockImage/20090117/inside-hard-drive-stock-picture-1040353.jpg

Its a much slimmer mechanism than a solenoid, and could be ideal for a shutter.

 

I'll look into that, I've got a few old hard drives hanging around