Electrical Engineering V2 - Developers

[QUOTE=jaooe;46197376]what would it take to detect metal within a quarter mile radius? and what would be the dangers of this in real life use??? :O[/QUOTE] A simple Buzzer connected to a battery should detect metal within a 1/4 mile radius. theres pretty much always gonna be metal somewhere, above ground or under it. After that, your looking at very precise radars for picking up small metallic objects.

[QUOTE=jaooe;46197376]what would it take to detect metal within a quarter mile radius? and what would be the dangers of this in real life use??? :O[/QUOTE] Well the logical extension would be building a magnet powerful enough to attract metal in a quarter mile radius. For that you will need a lot of liquid helium. Therefore dangers include: - -240°C freezer burn - Ripping pacemakers out of old people. - Growing a goatee and becoming evil.

[t]https://i.imgur.com/rQbVvWu.png[/t] Rocking out on Rock 101.1 FM. Now after I construct the 21cm directional antenna it becomes a matter of "how do I upload a snapshot (of data points) of a given spectrum to a database every minute". Back to the software thread!

[QUOTE=jaooe;46197376]what would it take to detect metal within a quarter mile radius? and what would be the dangers of this in real life use??? :O[/QUOTE] goddamn I read this and saw what would it take to detect quarters in a quarter mile radius and I'm looking at: [QUOTE]Well the logical extension would be building a magnet powerful enough to attract metal in a quarter mile radius. For that you will need a lot of liquid helium. Therefore dangers include: - -240°C freezer burn - Ripping pacemakers out of old people. - Growing a goatee and becoming evil.[/QUOTE] and I'm like bro quarters aren't magnetic I need to go take that nap now

Hey, so for anyone on here who knows about audio circuits, I've got a problem. Using the PA amp I got a while ago, I tried to hook up an electret microphone using this circuit I found on the web: [IMG]http://www.openobject.org/objectsinflux/images/FIX/Lamp-Parabolic%20Microphone/mic-circuit.gif[/IMG] I used a 3v coin cell, 1kΩ resistor a 4.7uf cap, and I've put I button from the mic ground to battery ground so that it only works when the button is held. Here's the issue: the only time I can get sound to come out is if I blow hard or tap the mic directly. The max input voltage of the amp is 4V, so I didn't want to use a higher voltage because I've already fried one of these, but would I be correct in assuming a higher battery voltage is needed?

I'm amazed how hard it is to find decent portable DVR's. Someone threw me a job to replace an old portapack reel-to-reel video recorder with a smaller and modern SD card solution. Everything coming out of china has two things going against them. -No triggering. You can disable motion detection but otherwise your REC start/stop is turning the DVR's power on and off. Pretty dirty. -You can't disable timestamps. A tube pickup camera will already have a low resolution image but in order to get rid of the DVR's forced timestamp you have to expand or crop out the stamp. The closest thing I could find was [url=http://www.ebay.ca/itm/191365017782]one of these pieces of junk.[/url] 640x480 (before cropping) at 15FPS (it can do 30 but the bitrate sucks) is about identical to the old Portapack. [media]http://www.youtube.com/watch?v=XNf9zl0akuY[/media] Now I need to order the DC/DC converters for the camera and recorder (did I mention the DVR drops out at 11.5v?) and design a shoulder strapped assembly to hold the recorder, converters, cabling and the 12V lead acid battery.

[QUOTE=papkee;46204449]Hey, so for anyone on here who knows about audio circuits, I've got a problem. Using the PA amp I got a while ago, I tried to hook up an electret microphone using this circuit I found on the web: [IMG]http://www.openobject.org/objectsinflux/images/FIX/Lamp-Parabolic%20Microphone/mic-circuit.gif[/IMG] I used a 3v coin cell, 1kΩ resistor a 4.7uf cap, and I've put I button from the mic ground to battery ground so that it only works when the button is held. Here's the issue: the only time I can get sound to come out is if I blow hard or tap the mic directly. The max input voltage of the amp is 4V, so I didn't want to use a higher voltage because I've already fried one of these, but would I be correct in assuming a higher battery voltage is needed?[/QUOTE] Try increase the resistor a bit. The amp may also be shit, you need a decent pre-amp for electret mics.

[QUOTE=Chryseus;46206140]Try increase the resistor a bit. The amp may also be shit, you need a decent pre-amp for electret mics.[/QUOTE] How does a preamp for an electret mic differ from a normal preamp?

[QUOTE=Chryseus;46206140]Try increase the resistor a bit. The amp may also be shit, you need a decent pre-amp for electret mics.[/QUOTE] Well the other device that I used to test the amp was an ipod, which I know has an output of around 2V, but I figured that was the purpose of the battery, to bring the voltage up enough.

[QUOTE=DrDevil;46206168]How does a preamp for an electret mic differ from a normal preamp?[/QUOTE] Not that much, although it depends how it's designed, not all pre-amps are suitable for all applications, in this case I think he's putting it directly in to a power amp. [QUOTE=papkee;46206954]Well the other device that I used to test the amp was an ipod, which I know has an output of around 2V, but I figured that was the purpose of the battery, to bring the voltage up enough.[/QUOTE] An electret microphone contains a small JFET amplifier to amplify the very small signal produced by the electret element, it doesn't provide much amplification so you need a decent pre-amp. Maximum output voltage of an electret is around 250mV depending upon the type and the value of resistor used which is insufficient to drive most power amplifiers directly. Something like this will do the job of a pre-amp just fine: [img]http://www.johnhenryshammer.com/TEChREF/opAmps/lectretMic.jpg[/img]

[QUOTE=pentium;46205161]I'm amazed how hard it is to find decent portable DVR's. Someone threw me a job to replace an old portapack reel-to-reel video recorder with a smaller and modern SD card solution. Everything coming out of china has two things going against them. -No triggering. You can disable motion detection but otherwise your REC start/stop is turning the DVR's power on and off. Pretty dirty. -You can't disable timestamps. A tube pickup camera will already have a low resolution image but in order to get rid of the DVR's forced timestamp you have to expand or crop out the stamp. The closest thing I could find was [URL="http://www.ebay.ca/itm/191365017782"]one of these pieces of junk.[/URL] 640x480 (before cropping) at 15FPS (it can do 30 but the bitrate sucks) is about identical to the old Portapack. Now I need to order the DC/DC converters for the camera and recorder (did I mention the DVR drops out at 11.5v?) and design a shoulder strapped assembly to hold the recorder, converters, cabling and the 12V lead acid battery.[/QUOTE] Would it be possible to use a dashcam in the setup? I've been using a G1WH dashcam for a while now and it has great quality and the settings allow you to disable motion detection and timestamps. It uses micro-sd cards though, also powered by standard 5v mini usb-b.

Nope. Client wants to specifically use a camera with a tube pickup.

[QUOTE=pentium;46207781]Nope. Client wants to specifically use a camera with a tube pickup.[/QUOTE] Your client is a moron then.

Heads up to anyone installing Atmel Studio, the certificate for the USB drivers installer seems to have expired so you'll need to change your system date to before 10/10 for installation until Atmel update it.

[QUOTE=Fuxed;46208652]Heads up to anyone installing Atmel Studio, the certificate for the USB drivers installer seems to have expired so you'll need to change your system date to before 10/10 for installation until Atmel update it.[/QUOTE] Whew, good thing CodeBlocks [I]easily[/I] integrates with WinAVR. :v:

[QUOTE=Chryseus;46207108]Not that much, although it depends how it's designed, not all pre-amps are suitable for all applications, in this case I think he's putting it directly in to a power amp. An electret microphone contains a small JFET amplifier to amplify the very small signal produced by the electret element, it doesn't provide much amplification so you need a decent pre-amp. Maximum output voltage of an electret is around 250mV depending upon the type and the value of resistor used which is insufficient to drive most power amplifiers directly. Something like this will do the job of a pre-amp just fine: [img]http://www.johnhenryshammer.com/TEChREF/opAmps/lectretMic.jpg[/img][/QUOTE] Awesome writeup, but I've got two questions because I know very little about electronics like this (even though this is pretty basic) 1: what would the output voltage be of this? I see Vin is 9V, but I'm assuming the resistors and the IC take it down to something lower. 2: Where would I place a switch to cut off the battery when not in use? Should I place it between the battery and the circuit?

[QUOTE=papkee;46211729]Awesome writeup, but I've got two questions because I know very little about electronics like this (even though this is pretty basic) 1: what would the output voltage be of this? I see Vin is 9V, but I'm assuming the resistors and the IC take it down to something lower. 2: Where would I place a switch to cut off the battery when not in use? Should I place it between the battery and the circuit?[/QUOTE] The output voltage depends upon the position of the gain potentiometer R5, it varies between roughly no gain to 100x gain, the maximum output signal would be roughly 2.1Vrms from a 9V supply. R1 supplies DC power to the internal amplifier of the electret mic, C1 allows the AC sound signal to pass through while blocking the DC. R2 and R5 are a feedback circuit that allows adjustment of the amplifier gain with the follow formula: Gain = -(R5 / R2) The gain is negative since the amplifier inverts the signal, hence this is called an inverting amplifier, this doesn't really matter though since it has no effect on the sound. The resistors R3 and R4 provide a constant 4V DC to the non-inverting pin of the op-amp, this ensures that the output of the op-amp stays at 4V DC with no signal applied. The AC signal which is amplified causes the output voltage to change, since the output voltage is held at 4V DC is can swing both positive and negative, although most op-amps can't go fully positive to the supply voltage, in this case around 7V would be the upper limit which gives a maximum swing of 3V peak (4V + 3V = 7V) which is 2.1Vrms. The capacitor C2 removes the DC from the signal so you only get the amplified AC out. As for a switch you can put it in line with the supply. You could use a lower voltage but I'd recommend 9V if you're using battery or 12V is you have a DC supply laying around, the current draw isn't that high so a battery should last a while.

has anyone noticed how insanely cheap Server PSUs are sold on ebay...... or rather, what people are missing out on? 12V 106.5A power supply.... for £15..... what utter madness is this? [url]http://www.ebay.co.uk/itm/261612609410[/url]

I think a lot of the reason people dont use server supplies more often for hobby stuff is because a majority of them do not have a cooling solution built in and rely on case flow from the servers fans to cool it. I have passed on using some supplies before simply because I didn't want to deal with retrofitting a fan to it.

[QUOTE=Tw34k;46223427]I think a lot of the reason people dont use server supplies more often for hobby stuff is because a majority of them do not have a cooling solution built in and rely on case flow from the servers fans to cool it. I have passed on using some supplies before simply because I didn't want to deal with retrofitting a fan to it.[/QUOTE] Also the cheap ones can be incredibly electrically noisy.

Zip ties, dude.

[QUOTE=metallics;46223539]Also the cheap ones can be incredibly electrically noisy.[/QUOTE] I wouldn't consider Delta Electronics power supplies cheap with poor EMI.

[QUOTE=Tw34k;46223427]I think a lot of the reason people dont use server supplies more often for hobby stuff is because a majority of them do not have a cooling solution built in and rely on case flow from the servers fans to cool it. I have passed on using some supplies before simply because I didn't want to deal with retrofitting a fan to it.[/QUOTE] Actually, having looked into it, many of them actually do, and it really isn't that hard to add a fan. Either way, look at the price difference: £20 + £5 fan = £25 £475 [url]http://uk.farnell.com/xp-power/hpu1k5ps12/power-supply-ac-dc-medical-12v/dp/1765290[/url]

[QUOTE=nuttyboffin;46224015]Actually, having looked into it, many of them actually do, and it really isn't that hard to add a fan. Either way, look at the price difference: £20 + £5 fan = £25 £475 [url]http://uk.farnell.com/xp-power/hpu1k5ps12/power-supply-ac-dc-medical-12v/dp/1765290[/url][/QUOTE] The price difference doesn't come from the fan. Your linked power supply from farnell is medical rated. Medical spec components, just as military spec are incredibly high reliability. Just check the price difference between a mil spec and a consumer LT1013 op amp. [url]http://uk.farnell.com/texas-instruments/lt1013cp/ic-op-amp-dual/dp/1470376[/url] [url]http://uk.farnell.com/texas-instruments/lt1013amjg/ic-op-amp-dual-precision-cdip8/dp/1459525[/url] [editline]13th October 2014[/editline] Also: The extra shit you have to put in your design to pass a medical approvals probably adds a lot more to the BOM than your regular 12 V supply. Not to mention how small the market is and how that affects the cost.

[QUOTE=alexaz;46224494]The price difference doesn't come from the fan. Your linked power supply from farnell is medical rated. Medical spec components, just as military spec are incredibly high reliability. Just check the price difference between a mil spec and a consumer LT1013 op amp. [url]http://uk.farnell.com/texas-instruments/lt1013cp/ic-op-amp-dual/dp/1470376[/url] [url]http://uk.farnell.com/texas-instruments/lt1013amjg/ic-op-amp-dual-precision-cdip8/dp/1459525[/url] [editline]13th October 2014[/editline] Also: The extra shit you have to put in your design to pass a medical approvals probably adds a lot more to the BOM than your regular 12 V supply. Not to mention how small the market is and how that affects the cost.[/QUOTE] Yes, i know that full well, but unlike other people, i don't have the time to really find a suitable comparison, but either way, you are actually looking at around that price. Oh look: [url]http://uk.rs-online.com/web/p/embedded-switch-mode-power-supplies-smps/7646943/[/url] That would be a decent quality one, probbibly just as good, maybe even worse then the delta one. Heres a cheap chinese one: [url]http://www.aliexpress.com/item/1200W-12V-Single-Output-Switching-power-supply-for-LED-Strip-light-AC-to-DC/621546637.html[/url] That is still more expensive, and still gonna be awful quality. Over all. Really, Computer Switchmode PSUs are actually rather damn good, expecially the server ones, after all, they are designed for very high reliability.

So in school we had to use optical fiber or do wireless for communication. I decided to opt for optical fiber and do some bit banging across 2 MSP430's. [img]http://dl.dropboxusercontent.com/u/100328/Facepunch/pic1%20resized.jpg[/img] [img]http://dl.dropboxusercontent.com/u/100328/Facepunch/pic2%20resized.jpg[/img] [img]http://dl.dropboxusercontent.com/u/100328/Facepunch/TEK0000.BMP[/img] Quite bad report, but w/e [URL]https://www.dropbox.com/s/m0iqqawgtcpyawj/Mads Stark Optic and Wireless communication Report.pdf?dl=0[/URL]

Got some new hardware to play with! STM32 arm microcontrollers from ST :) (Cortex M-0, Cortex M-3, Cortex M-4) [IMG]http://dl.dropboxusercontent.com/u/100328/Facepunch/Billede 14-10-14 17.55.25.jpg[/IMG] [IMG]http://developer.mbed.org/media/platforms/ST-Nucleo-L152RE-Arduino.png[/IMG] [IMG]http://developer.mbed.org/media/uploads/screamer/st-nucleo-l152re-morpho.png[/IMG] Lots of IO to work with! and this pinout is for the smallest nucleo board with the cortex m-0

[QUOTE=AGMadsAG;46231380]Got some new hardware to play with! STM32 arm microcontrollers from ST :) [img]http://dl.dropboxusercontent.com/u/100328/Facepunch/Billede%2014-10-14%2017.55.25.jpg[/img][/QUOTE] How much did that lot cost you?

[QUOTE=ben1066;46231391]How much did that lot cost you?[/QUOTE] Around 65 kr. each, which is around 10$ each. + 10$ for shipping. They're bought from Farnell.. element14 whatever they wanna be called.

[url]http://www.aliexpress.com/item/Free-shipping-ESP8266-serial-WIFI-wireless-module-wireless-transceiver/2031529724.html[/url] So I think I'm gonna order a handful. Some info: [url]https://nurdspace.nl/ESP8266[/url]