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NEED HELP wireless oscilating electromagnet

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jhelzer10

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8DC6B36C-CC0A-4C00-9371-F46282CF759C.jpeg 794974F7-ADF7-495A-B95D-D7130DE854F8.jpeg 3583B706-1C37-4734-AF35-21A3A72A4AC0.jpeg 58D78FFE-22E2-421A-B39D-6B9C73F4ADE1.jpeg D9E9FC37-9294-43A6-96ED-7BF60E17F048.jpeg Hello, i am new to electronics. I have a basic knowledge of electronic components and how they work. But i lack the knowledge of calculations and applying the right components with propper values.

I have constructed a wireless oscilating electromagnet. Im using a 9v 555 pulse module to send data to a 433mhz rf transmitter. I have got this end of the circuit to function quite well. But the recieiving end not so much. The 433mhz receiver is 5v. So im using a 7805 voltage regulator to step down voltage from 9v battery. Then the data from the receiver is connected to a 1k ohm resistor then to the base of a tip120 darlington transistor. The reason im using a darlington is because i want as much current as possible flowing through the EM coil. Everything works i just have a few issues. I cant get a full range of adjustment of frequency with the 555 pulse module. Im not getting enough current through the coil. Sometimes the darlington transistor gets hot. And the permanent magnet and the EM coil make this god awful screetching noise when its pulsing. It sounds like a tuning fork and i can actually feel the permanent magnet vibrating at high frequency. Ive tried hooking up more 9v batteries in parralell to boost the current but then i have problems with overheating the transistor. I was under the impression that a transistor acts as an amplifier as well as a switch. So why is it that when i hook the EM coil directly the the batteries i get the amount of current i want. But when the EM coil in wired in the pulsing circuit with the same amount of batteries the strength of EM field is less? Shouldnt the darlington transistor amplify the current? I know there is alot that im missing. Would really appreciate any help i can get. Thanks!
 

throbscottle

Well-Known Member
Welcome to ETO and congratulations on building working pair of circuits!
First question, why do you have a permanent magnet inside your electromagnet? What's happening is it's acting like a loudspeaker, so the "god awful screeching" is the sound being created by your 555 timer (or something like it anyway).
Since you are pulsing current through the solenoid, you should have a diode connected across it with the cathode connected to +9v and anode to the transistor's collector. This will allow the solenoid's back-emf to flow and improve efficiency.
Fit a heatsink to the transistor so it doesn't suffer too much by heating up
The signal you are getting out of the receiver might not have such good rise and fall times as you would like, so it might be causing the transistor to be in linear mode longer than you hoped for. Possibly you can improve the situation by connecting another resistor between the transistor's base and 0v (your "-" terminal). I would try 220 ohms to start with and experiment from there. It won't make it faster but it will help to turn the transistor off when the receiver's output goes low.
Not knowing anything about the 555 timer pulse module, all I can say is you shouldn't be expecting a wide range of frequency from it. The frequency of a 555 timer in astable mode is controlled by 2 resistors and a capacitor, so it's a little complicated to vary frequency and keep the same mark-space ratio.
 

rjenkinsgb

Well-Known Member
Most Helpful Member
I think part of the problem is that you need decoupling capacitors on the power rails - both the +/- 9V and between the 5V and -ve.

Without those the whole circuit may be oscillating.
I have even seen a 7805 regulator malfunction because there was a few inches of wire between the IC and the circuit board with the capacitors, rather than the caps being on the IC pins... Things like that can be very critical.

Also note that a 7805 will start to reduce output if the input voltage gets below 7V, while a "9V" battery will run down to 6V over its normal life before being fully exhausted. To guarantee proper operation of a 5V circuit on a 9V battery you need a "low drop out" regulator.

See these examples - what I'd think of as basic decoupling:
https://i.stack.imgur.com/cBfLI.png

And high-grade decoupling to handle both current variations and high-frequency noise:
https://reviseomatic.org/help/e-components/Circuit-7805-Regulator-SPE.GIF
 

jhelzer10

New Member
The reason i am using a permanent magnet is because there is a lot more force between the electro magnet and the permanent magnet, vs a solid iron part for the acuating part of the solenoid. I would rather use a piece of iron because its easier and cheaper, but it just seems like theres not enough force.
I will try the clamp diode, im just unsure of the exact diode to use? I have a bunch of n4007’s, will these suffice?
I posted a photo of the 555 module that im using, hope that helps.
So when you say put a resister from the base to the 0v terminal you mean from base to the emitter? And is that in series or parallel?
I will definitely try the capacitors with the voltage regulator! That seems to be whats happening is the whole circuit is oscillating.
This was a ton of help! I appreciate the insight! Totally not worth tearing my hair out trying to tackle it on my own. Thanks guys.upload_2018-6-25_11-31-11.jpeg
 

throbscottle

Well-Known Member
I think I have mis-understood the purpose of your circuit, as I thought you were using the 555 as an oscillator and doing something involving some kind of frequency with your solenoid. So you are using it to send on or off states, so the solenoid should be either on or off, and not oscillating?
In which case you definitely need those decoupling caps!
1N4007 would do, just, but you'd be better using faster diode such as 1N5819 (or one of it's higher voltage cousins) or a high speed rectifier.
Yes, base to emitter, though to be honest if the "off" condition of your receiver's output is below 1.2V you needn't worry about it since this is below the transistor's turn on voltage anyway.
 

jhelzer10

New Member
Yes i am using the 555 pulse module to send out frequency wirelesly to make the electromagnet oscilate at same frequency as the 555 module. Exscuse my lack of terminology, i guess its not an acuator, its an oscilator. It seems to be working just fine, its just that when i adjust to the higher frequencies, the electromagnet goes into a steady state. This isnt too big of deal tho. It is operating within the frequency range that i need. Was just curious if there was any way i could fix that. I will try the higher voltage diode cause when i tried clamp diode before it would get too hot.
 

throbscottle

Well-Known Member
Not higher voltage - the 1N4007 is already rated for 1000V! But it was designed for rectifying power from mains transformers, not for fast switching. Higher speed is what you need. The 1N5819 is a Schottky rectifier so it should be plenty fast enough. If the diode is getting hot maybe you have it connected the wrong way? It has to be the opposite direction to current flow when the transistor is on (ie, with cathode to battery +), so when the transistor turns off the solenoid will now be generating a current as it's magnetic field collapses, and the diode will conduct that until it decays away.
So, why do you want to make the solenoid oscillate? It's an unusual thing to want to do.
 

jhelzer10

New Member
Ok i ordered shottky diode and heat sink for transistor. Will apply those to my circuit and also the protection caps on the voltage regulator.
The reason for this oscillating solenoid is i am conducting an experiment with water waves and this is going to be a water wave generator. I need to be able to create different frequencies of water waves, wirelessly.
 

throbscottle

Well-Known Member
Ah, that makes sense now. Hence you need a powerful solenoid. Will be interesting to see how it turns out.
 

throbscottle

Well-Known Member
Firstly, if possible, make sure your receiver is tuned to the exact frequency of the transmitter, if you have any way to adjust it. Apart from that, it's getting into stuff I don't really know about, but you need to learn to tune your antennae. There's plenty of good information on the web, just look for "antenna tuning". Good luck!
 
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