Need help with modifying a bistable flip-flop circuit - Page 1
Forum section: electronics / beginners

author: jerred
author_rank: Contributor
timestamp: October 25, 2014, 03:58:51 am
content: Hi, I am new to the site and I am looking for help in modifying the bistable flip-flop circuit that contains LEDsso that it will look like the bistable flip-flop circuit with the reed relays (they have internal diode across the coil).Do I need to change any of the component values, add on/or replace any, and which type of transistorwould be best? Any help would be appreciated

author: Pillager
author_rank: Unknown
timestamp: October 25, 2014, 07:55:22 am
content: Have you tried to build the original circuit?

author: fcb
author_rank: Super Contributor
timestamp: October 25, 2014, 10:46:46 am
content: Try it and find out. If the original worked, then this is likely to work to.Probably worth explaining what you are trying to drive (? "to inverter" ?) as there maybe a better way to achieve your end goal.

author: jerred
author_rank: Contributor
timestamp: October 25, 2014, 05:29:08 pm
content: To Pillager: I haven't tried to build the original circuit yet, as I was unsure of what transistor to use, and didn't want to risk damaging the reed relays.To fcb: I am using the inverters to power small pieces of EL panel, which will be used as a light source for two irregular-shaped cutouts in a project I am working on. They would be at power up; left panel on, right panel off. When the flip-flop circuit received a single pulse, the left panel would be off and the right would be on. They would only change when a pulse is received from the timer circuit. That part of my project is already figured out. I have a single shot delayed timer circuit that would send a pulse to a reed relay built into it that would provide the simulated button press to activate the flip-flop circuit. The flip-flop circuit was the problem as all the solutions I could find in per-built circuits all used a standard relay that turned on or off a single output. I hope this helps. Thanks.

author: oldway
author_rank: Super Contributor
timestamp: October 25, 2014, 05:51:43 pm
content: To protect the transistors against peak comutation voltage (inductive load), a fast free wheeling diode is needed in // with each reed relay.As current is low, you can use two 1N4148.

author: jerred
author_rank: Contributor
timestamp: October 25, 2014, 08:36:36 pm
content: The reed relays have a built-in diode, so an external diode isn't necessary. I do need to know which type of npn transistor wouldwork for the modification, and whether any of the capacitors or resistor values would need to be changed, or if they could stay the same. I would like to order the parts I will actually need, since it takes several weeks to receive them (I order them on eBay since there aren't any local sources for components that are not expensive.) Thanks.

author: Tandy
author_rank: Frequent Contributor
timestamp: October 25, 2014, 09:11:55 pm
content: First of all you will need to know the current required to energise the relay coil so that you can get a transistor with a Maximum DC Collector Current capable of switching the required current.You will also need to know the resistance of the reed relay coils so you can set the resistor values accordingly, you will likely need to increase the base resistor values to set a suitable discharge time of the capacitors.PS if you fill in your country on your profile someone might provide you with links for sources for components.

author: jerred
author_rank: Contributor
timestamp: October 25, 2014, 09:43:11 pm
content: The reed relays were purchased on eBay -http://www.ebay.com/itm/10pcs-12V-Relay-SIP-1A12-Reed-Switch-Relay-4PIN-for-PAN-CHANG-Relay-/131317611933?pt=LH_DefaultDomain_0&hash=item1e9323bd9dI am in the U.S., and I unfortunately have no other information on the reed relays other than what is listed on the site.They are listed as 12V reed relays, which I assume means they need 12V to energize the coil to close the contacts. Beyondthat, I haven't a clue, which is why I was requesting assistance so I don't end up blowing up one or more components.Thanks.

author: Tandy
author_rank: Frequent Contributor
timestamp: October 25, 2014, 10:17:56 pm
content: Current in Amps = Power in Watts / VoltsFrom the link you gave the relay is 144mW (0.144 Watts) nominal input power. So 0.144/12 = 0.012A 12mA so the power requirements are not very high so you could use the common 2N2222aThe resistance of the coils are shown as 1K so the 7.5K resistors shown on the original circuit diagram will probably be adequate.

author: Zero999
author_rank: Super Contributor
timestamp: October 25, 2014, 10:54:39 pm
content: How much power do the inverters need?What about using transistors instead of relays?Why are you using a relay to trigger the circuit? If the timer is run off the same power supply as the bistable then why not AC couple the pulse to the transistor emitters via a suitable capacitor?

author: jerred
author_rank: Contributor
timestamp: October 25, 2014, 11:07:58 pm
content: To Tandy:So, if I understand correctly, the modified version of the flip-flop circuit can be built as pictured without any additional parts required, using the same values on the resistors and capacitors.To Hero999:The Inverters are 3V DC, being used to power two separate small EL panels. The flip-flop circuit is powered by 12V DC, so the two need to be kept separate. I also needed to keep it as simple as possible due to limitation of space for the circuits in my project.

author: IconicPCB
author_rank: Super Contributor
timestamp: October 26, 2014, 01:40:07 am
content: You will find the presence of inductive loads in the collector of the two transistors may affect the frequency of oscillation adversely.A better approach would be to retain the LED circuit and use a couple of transistors to buffer the two outputs and rive reed relays independently of the flip flop

author: jerred
author_rank: Contributor
timestamp: October 26, 2014, 02:57:31 am
content: To IconicPCB:"A better approach would be to retain the LED circuit and use a couple of transistors to buffer the two outputs and rive reed relays independently of the flip flop"I don't quite get what the word 'rive' means, unless it is a typo. Since the original circuit diagram is not my design, I wouldn't know where the additional transistors would be attached. If it turns out to be that a major redesign of the original circuit is needed to make it work, it might be simpler to go with my original idea. That was to build the one-shot delay timer circuit Ialready had the working diagram for, and replace the standard relay at the output with a solenoid to physically push a DPDT latching pushbutton switch to accomplish the same thing. The flip-flop idea was just to make the whole assembly as non-mechanical as possible. I do appreciate your input, as it probably saved me the time and materials building a circuit that probably won't work the way I hoped.

author: IconicPCB
author_rank: Super Contributor
timestamp: October 26, 2014, 03:25:01 am
content: rive = drive...My apologies

author: SeanB
author_rank: Super Contributor
timestamp: October 26, 2014, 08:35:46 pm
content: They are likely 1k coils, so will work there as is. Your transistors can be any NPN transistor like a PN2222, or similar, or pretty much any NPN transistor in a TO92 package that you can find 2 off on a board or locally in used electronics.Datasheet for a relay that yours are likely clones ofhttp://aitendo3.sakura.ne.jp/aitendo_data/product_img/wireless/SIP-1A12/SIP-1A12.pdf

author: jerred
author_rank: Contributor
timestamp: October 26, 2014, 09:30:01 pm
content: To SeanB:Thanks for the info. I wasn't sure if I could use the same components as the original circuit with the LEDs. I was going nuts trying to find an alternative solution.

author: jerred
author_rank: Contributor
timestamp: October 26, 2014, 09:44:20 pm
content: To SeanB:Thanks for the info. I wasn't sure if I could use the same components as the original circuit with the LEDs. I was going nuts trying to find an alternative solution.

author: Zero999
author_rank: Super Contributor
timestamp: October 27, 2014, 07:50:34 pm
content: Quote from: jerred on October 25, 2014, 11:07:58 pmIs there any reason why you can't power the bistable off 3V?

author: jerred
author_rank: Contributor
timestamp: October 28, 2014, 12:45:06 am
content: To Hero999:I assumed that since the original circuit diagram stated a voltage range from +6V to 12V for the circuit, it wouldn't function at a lower voltage correctly. Since I don't have the specs for the 3V DC inverters I will be using, I felt it would be safer to isolate them from the delayed timer - flip flop circuit.

author: Zero999
author_rank: Super Contributor
timestamp: November 01, 2014, 11:05:34 pm
content: What's to say ot won't run off 3V?

author: jerred
author_rank: Contributor
timestamp: November 02, 2014, 01:54:33 am
content: To Hero999:Where did you find the circuit diagram? That is exactly what I was looking for!! Thanks so much!!!Just one question; what type of transistor is used at the top of the circuit near the load?

author: Kappes Buur
author_rank: Regular Contributor
timestamp: November 02, 2014, 03:59:41 am
content: Quote from: jerred on November 02, 2014, 01:54:33 amUse the 2N2907 or 2N2907A as the complement to the 2N2222 or 2N2222A.

author: jerred
author_rank: Contributor
timestamp: November 02, 2014, 06:58:19 am
content: To Kappes Buur:Thanks for the info on the transistor type. I really, really appreciate it.