using a logic pulse to ring a bell? - Page 1
Forum section: electronics / beginners

author: edb1984
author_rank: Contributor
timestamp: January 27, 2014, 01:32:17 am
content: Hello EveryoneI have been watching the EEV Blog videos on Youtube for some time and have been "tinkering" with electronics on and off as a complete amateur for a few years, i have ZERO knowledge of my own and follow others guides as a general rule.i have been making some Nixie, VFD and LED clocks for the past few months and i have a question that i cant find an answer to and i was hoping you might be able to help out.i have built a few Single digit nixie clocks from this websitehttp://www.electronixandmore.com/projects/nixieclocks/3.htmland although i have managed to build it fine, i wanted to use the Logic pulse to drive a servo or something similar to strike a bell to indicate the hour.his design states that"NOTE: There is a chime logic pulse output on pin 2 (RA3). The logic output will give a number of pulses in accord to the hour when the minutes turn to zeros. For instance, there are 8 logic pulses from pin 2 when the time turns to 8:00. The output is not an audio frequency, it is a simple logic pulse, so one would need an tone or chime generator for the audio."is there any simple way of converting this into a output to strike a bell? i have emailed the author of the guide but had no reply so maybe you could help out? if there is a way of converting this output, where would i find a schematic?if not, does anyone know of a guide or similar for me to build a clock that will manually "strike" the hours? i have searched the net high and low but cant seem to find anything relevant.i like this design because it is simple and although i am jumping on a bandwagon i love VFD / Nixie tubes.please forgive my ignorance and any silly questions, like i said - i can follow a guide well but have ZERO knowledge.many thanks in advance!

author: Psi
author_rank: Super Contributor
timestamp: January 27, 2014, 01:39:05 am
content: If the pulse length and repeat rate is long enough (250ms or more) you could use the pulse to drive a transistor or logic level mosfet.The transistor or mosfet gives you enough current to drive a solenoid which would move its actuator forward every time the pulse occurs.If you put a bell in front of the actuator it would give it a good whack.First thing to check is how fast these pulses on RA3 are.If they're intended for this sort of thing they should be nice and slow so the solenoid has time to move back and forward.An easy way to check the pulse length and repeat rate is to connect an LED and 1K resistor in series between VCC and RA3.You will then be able to visually see it flash and check if the speed is slow enough and the pulse length long enough to move something mechanical.If you use a solenoid make sure you have a protection diode in the circuit.Any good youtube/google circuit example for driving a solenoid or relay should have this but if its missing it may damage the chip.

author: Rigby
author_rank: Super Contributor
timestamp: January 27, 2014, 01:43:17 am
content: You would need to use the logic pulse to switch a transistor on and off, the transistor operating something that can ring a bell, or something on the other end of that logic pulse that can do something with the pulse.There is a YouTube user called "Afrotechmods" that has a video on MOSFETs which will show you how it is done, if I am remembering correctly. Actually, it may have been Ben Krasnow. Maybe both... There are literally hundreds of videos on Youtube describing this. Some of them are even educational.

author: edb1984
author_rank: Contributor
timestamp: January 27, 2014, 03:12:51 am
content: Quote from: Psi on January 27, 2014, 01:39:05 amTHANKS! - i just tested that theory and you can watch the below video i recorded with the TOP RED LED wired up to VCC/RA3 and you can see a slow pulse length of "off" flashes "or un-flashes???"(please dont ask about my circuit layout for this one! i have made a few and i have started messing around with having the parts floating about so you can see what is connected to what etc - its what i like about the NIXIES and VFD's - the fact you can see all the insides)Now here is the part where i become a nuisance, how would i wire this up to a solenoid? what parts? what layout? what values? - does anyone have any recommendations of how and where to research this more?Again sorry to ask what are probably simple questions! and THANKS AGAIN!

author: Psi
author_rank: Super Contributor
timestamp: January 27, 2014, 05:47:19 am
content: sorry, yeah, i dunno why i said VCC instead of GND. (that's why the flashing is reversed)Doesn't matter though, it proves that the flash rate is perfect for a solenoid.First you need to find a small solenoid that will run on the voltage you have available, 12V, 5V etc.. Small ones draw 0.5 - 2A, so check your power supply can handle that.If you have, for example, 12V which is regulated to 5V to power the MCU you should use a 12V solenoid powered from your 12V.If you cant find any solenoids you may be able to dismantle anylargerelay you have in your junk box and remove the switch contacts. Then bend the contact arm so it hits the bell. It wont hit with as much force as a solenoid but it will work if the bell is large.Now you need a "N channel logic level MOSFET".Something in TO220 packaging will usually have plenty of power for a solenoid, get one that can handle over 40V and over 10A (most will).(Post some part numbers you have, or can get at your local electronics store, and we can confirm if they will work.)Two resistors, 2000 ohm and 220 ohm should work fine.One diode. (for a small solenoid a generic 1N400X diode will work. If the solenoid is large use a larger 1N540X diode, (the X number doesn't matter)Wire it up like this

author: edb1984
author_rank: Contributor
timestamp: January 27, 2014, 01:50:35 pm
content: Quote from: Psi on January 27, 2014, 05:47:19 amThats great! thanks so much!one last questioni have not worked with Solenoid's before, i know there are different types - so would i be correct in thinking i would need a Push type? and as it gets the signal it would push out only once, then as the signal stops retract back in?i have found this one on ebayhttp://www.ebay.co.uk/itm/TAU-090-DC-12V-0-25N-3-8mm-Push-Type-Open-Frame-Solenoid-Electromagnet-/191025318411?pt=LH_DefaultDomain_3&hash=item2c79ff0a0bThe power supplies are salvaged 12V 1A mains to dc plugs i got from work that use to power a load of old modems so i think the power would be ample to power the clock and the solenoid ?for the Mosfet, i have a load of irf3205 's, am i correct in thinking that should work okay for this application?Thanks again, i didn't think i would get an answer so fast or precise! but you have proved me wrong! -a thousand thank-you's!

author: psycho0815
author_rank: Regular Contributor
timestamp: January 27, 2014, 02:30:33 pm
content: the mosfet looks generally ok, it's not logic level though.From what i can tell from the datasheet you should be able to get enough current through at 5V Gate-Voltage but you would have to try.

author: edb1984
author_rank: Contributor
timestamp: January 31, 2014, 04:50:16 am
content: Thanks so much everyone for your help, use some salvage parts from a microwave to make the electronics to ring the bell (and used the timer bell as well)see video below, Thanks Again!

author: GreyWoolfe
author_rank: Unknown
timestamp: February 01, 2014, 01:40:38 pm
content: pretty cool!