Switch 9v with 3v - Page 1
Forum section: electronics / beginners

author: tompl
author_rank: Contributor
timestamp: November 04, 2017, 09:00:52 pm
content: HiI'm looking to switch 9v with 3v ideally with I2C as im planning to control it via a esp8266 im looking to do it for 32 channels is there any component out there that will do this?Just to give you idea i want to launch fireworks next year using a simple 9v battery. just likehttp://pyrostation.com/?product=launch-kontrol-pulseTom

author: tompl
author_rank: Contributor
timestamp: November 04, 2017, 09:42:16 pm
content: I'm thinking 2xMCP23017 with 32xRLB8721PBF

author: Zero999
author_rank: Super Contributor
timestamp: November 04, 2017, 09:49:12 pm
content: How much current?What sort of 9V battery is it? A tiny little PP3 battery can't provide much current, just over 1A peak and 150mA continuously.https://cellpacksolutions.co.uk/wp-content/uploads/2015/06/ultralife-u9vl-jp-technical-data-sheet.pdf

author: tompl
author_rank: Contributor
timestamp: November 04, 2017, 09:55:08 pm
content: Just a normal alkaline PP3 battery it only needs to be on for 150 ms.

author: Zero999
author_rank: Super Contributor
timestamp: November 04, 2017, 11:53:40 pm
content: http://www.onsemi.com/pub/Collateral/NCV7608-D.PDF

author: Raj
author_rank: Frequent Contributor
timestamp: November 05, 2017, 08:54:52 am
content: Just about any raspberry pi i2c gpio expander will do

author: Ian.M
author_rank: Super Contributor
timestamp: November 05, 2017, 10:33:00 am
content: Quote from: Raj on November 05, 2017, 08:54:52 am.... if you want to blow up your Pi or ESP8266. The minimum to do it reliably would be to have the I/O expander drive a beefy logic level N channel MOSFET on the low side of the firing circuit for each channel.Without knowing the ignitor resistance, no-one has any idea how much current is required for the firing pulse. We don't even know if the launch controller linked to by the O.P uses a supercap or similar to allow the firing pulse to be much higher current than a PP3 battery can directly supply.

author: tompl
author_rank: Contributor
timestamp: November 05, 2017, 03:58:25 pm
content: I can't see any caps but if it helps here is the lunch quntrol board

author: Ian.M
author_rank: Super Contributor
timestamp: November 05, 2017, 04:12:43 pm
content: Well that board appears to be very simple. Its just switches and indicator LEDs.Can you measure the resistance of an igniter? Caution: there is a risk of it igniting so don't use an analog meter and don't use one that uses a high test voltage. Use long enough wires that you don't have to hold the igniter, and place the igniter on a flameproof surface while testing it.

author: tompl
author_rank: Contributor
timestamp: November 05, 2017, 04:32:38 pm
content: Ok so I tried to test it but it seems to be the same resistance as just connecting the leads together :/ may need a better multimeterCould it be 0

author: Nusa
author_rank: Super Contributor
timestamp: November 05, 2017, 05:13:18 pm
content: I'd suggest opto-isolated relays. These can be made or can be found in ready-made modules with multiple channels. So basically you provide a signal to the opto-isolator, which then provides an isolated signal from a relay battery to operate the relays, which in turn switches power from the igniter battery to the igniter.Here's a decent overview of what I just said:https://arduino-info.wikispaces.com/RelayIsolationHaving multiple batteries to insert/turn on before the system operates is a good thing from the safety point of view. I hope you put some real security in the wifi software as well, so nobody hijacks your explosives.

author: Zero999
author_rank: Super Contributor
timestamp: November 05, 2017, 05:39:46 pm
content: Quote from: tompl on November 05, 2017, 04:32:38 pmOf course it can be zero Ohms. It's just lower, than your meter can detect.It sounds like it will take more current than a PP3 battery can provide.

author: IanB
author_rank: Super Contributor
timestamp: November 05, 2017, 05:46:48 pm
content: Quote from: Hero999 on November 05, 2017, 05:39:46 pmIf you short a 9 V battery against wire wool I think it gets red hot and ignites? So such a battery could provide enough energy in short pulses to ignite a fuse, if the igniter was designed with that power source in mind.

author: tompl
author_rank: Contributor
timestamp: November 05, 2017, 05:51:40 pm
content: I know the clips work I used them last night

author: Zero999
author_rank: Super Contributor
timestamp: November 05, 2017, 05:55:39 pm
content: Quote from: IanB on November 05, 2017, 05:46:48 pmYes that will work because only a low voltage is required across the wire wool, but this isn't wire wool. It's a specially designed fuse and we don't know what voltage is required for it to ignite. Even then, the controller still needs to carry on working, so the battery voltage can't drop too low.

author: tompl
author_rank: Contributor
timestamp: November 05, 2017, 07:33:51 pm
content: So something like thishttp://uk.farnell.com/oeg-te-connectivity/oje-ss-103hm-000/relay-spst-no-250vac-30vdc-10a/dp/1891660?

author: tompl
author_rank: Contributor
timestamp: November 05, 2017, 07:54:57 pm
content: So something like thishttps://easyeda.com/thomaspleasance/Fireworks-d3a72819f4aa4d7ca8863818c1c3703c