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Actually yeah when I plug the values into my calculator I get about 1200Hz. 1/(ln2*140000*10E-9) = ~1202Hz. Either my oscilliscope is jacked-up or something else is at work. I'll try better diodes anyways but something freaky is definitely going on. Edit: Derp at some point I switched it to a 1nF capacitor and forgot. Doesn't explain the frequency variance though. Edit2: At 10nF it actually seems stable over all duty cycles. Huh. I'd prefer it to not get wonky at higher frequencies, can something be done about that? Better diodes? Or is there a lower limit on the value for the capacitor? BattleMaster fucked around with this message at 03:01 on Apr 13, 2011 |
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Apr 13, 2011 02:54
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I don't know if the 555 hates small capacitors, but it might be worth it to use the 10n cap and lower your resistance to match. There could be some capacitances in the IC that appear much greater next to 1nF than 10nF. Also that particular 1n cap may have some strange parasitics/nonlinearities that aren't as significant in the larger one.
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Apr 13, 2011 03:05
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Slanderer posted:Hah, I didn't even notice that. I assume he hooked it up right when trying it, though... No 
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Apr 13, 2011 03:05
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I tried a 5k pot and 200 ohm resistors with that same 10nF capacitor and it definitely varies wildly in frequency as the pot varies. Replacing the capacitor with a 100nF one causes the frequency to be very stable at about 4kHz but it jumps up to 5kHz at very close to minimum duty cycle. I'm going to pick up some better diodes just in case but other than that I don't have a clue. BattleMaster fucked around with this message at 03:13 on Apr 13, 2011 |
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Apr 13, 2011 03:11
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BattleMaster posted:I tried a 5k pot and 200 ohm resistors with that same 10nF capacitor and it definitely varies wildly in frequency as the pot varies. Replacing the capacitor with a 100nF one causes the frequency to be very stable at about 4kHz but it jumps up to 5kHz at very close to minimum duty cycle. What is the voltage rating and material of the capacitor?
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Apr 13, 2011 16:48
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SnoPuppy posted:What is the voltage rating and material of the capacitor? Ceramic and 50 volts. I read in the application notes for the 555 that they recommend tantalum but I didn't think it would make such a difference.
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Apr 13, 2011 17:04
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BattleMaster posted:Ceramic and 50 volts. I read in the application notes for the 555 that they recommend tantalum but I didn't think it would make such a difference. It might, it might not. Ceramic caps do tend to change their capacitance when DC bias is applied - a crappy ceramic (like a Y5V material) might loose 20% of it's capacitance at 6V on a 50V rated part. They also can have some hysteresis effects, but that would probably be negligible at your charging rates/voltages. I'd try to swap out the ceramic 10nF for a different material 10nF to see if it's the cap. Then I'd look at switching the diodes to a schottky.
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Apr 13, 2011 17:37
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SnoPuppy posted:It might, it might not. Cool, thanks. Decreasing capacitance would definitely account for the increase in frequency. I'll go out shopping on the way home tonight and see if swapping out the capacitor and diodes makes a difference.
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Apr 13, 2011 18:45
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Sorry for the second post in a row but I have an update! I switched up the capacitor for a tantalum one and the frequency is definitely much more stable now. The variance seemed to drop even further with some faster Schottky diodes (BAT46) as well. Thanks, everyone, for all the help. I thought the diodes were suspect but I had no clue that the capacitor mattered so much!
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Apr 14, 2011 00:38
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Cool! Reading you fight with the 555 has made me realize I am fairly ignorant about the innards. Does anyone know of a particularly good explanation on what's going on on the inside?
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Apr 14, 2011 03:04
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Delta-Wye posted:Cool! Reading you fight with the 555 has made me realize I am fairly ignorant about the innards. Does anyone know of a particularly good explanation on what's going on on the inside? I've built one from discrete components before. It's very simple but a pretty clever piece of work all the same. Here's a diagram taken from the Philips 555 Timer Application Notes:  Those three resistors are all valued 5k ohms (hence the name "555"). They create reference voltages of 1/3 VCC and 2/3 VCC for the two comparators. When the voltage on Trigger is below 1/3 VCC the flip-flop sets making the output high. When the voltage on Threshold is above 2/3 VCC the flip-flop resets making the output low. When the output is low the discharge pin sinks current. The control voltage pin allows access to the resistor divider. Oftentimes people just put a bypass capacitor between it and ground for stability (or just leave it alone altogether) but I've seen it used to implement feedback when used in DC-DC converters. Reset resets the flip-flop when brought low. The 555 timer doesn't make a lot of assumptions about what you are going to use it for so it can actually be used for a good many different things. The document I linked above goes over many of them. The configuration I'm using is a modification of one of the typical ones known as astable, which acts as a free-running oscillator.  When set up this way, the 555 timer constantly charges and discharges a capacitor as a time base. It outputs high while it charges the capacitor through resistors RA and R to 2/3 VCC, then outputs low as it discharges the capacitor down to 1/3 VCC through resistor R, at which point the output goes high again and the capacitor begins to charge and the cycle begins again.  The typical configuration charges the capacitor through both resistors and discharges it through only one. This restricts the duty cycle to 51% or greater. I'm using the above configuration (with a potentiometer and a pair of resistors rather than two discrete resistors), which uses a couple of diodes to allow the charge and discharge paths to be independent of each other allowing a full 1% to 99% (it's actually not healthy for the timer for either resistor to be very low resistance) range of duty cycle. BattleMaster fucked around with this message at 03:50 on Apr 14, 2011 |
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Apr 14, 2011 03:45
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Hi! So I have this idea, and while I've done some embedded work I've never spanned so many levels (I'm an FPGA guy at work). I'd like to hear input from your collective knowledge to help me decide if this is A) possible, and B) the best way to go about trying to do it: I want to create a wireless transmitter/receiver (although it could be wired if it had to be) for the video signal of a dSLR that is output to the LCD backscreen as it is recorded. I want to capture that signal and put it to an OLED or LCD display. Preferable something I could mount to the inside of some beefy sunglasses or a collar or something. The idea is that I want to put my camera on the end of a pole, record video and be able to see what I'm recording from that point of view while I'm doing it. Eventually some extra controls and a focussing harness to remotely focus while doing this would be the ultimate goal. 1) does this sound at all possible? I know it's possible to grab video over USB (at least from a Canon 40D) - this program does it and I've used it in the past. Obviously the problem is that I want to do this without a huge computer at either end of the system. 2)How should I go about it if it is possible? specifically: a) where should I start on researching how to capture Canon dSLR video over USB? b) how would I capture that data on the transmitter side? c) how would I power a device like this? Obviously this is tackling a lot of stuff I've never done before but I'd be very happy to work it out part by part over a long period of time. I would imagine that either getting some kind of OLED display and learning how to output any video signal onto that would be a useful start. Or perhaps on the other end - trying to capture the data from a dSLR with a computer first? Suggestions? Help? edit: well. That's no fun. I guess it's possible. Now, how to go about it on my own? edit 2: well ok - looking at that thing it's immediatly obvious that I don't need to try and capture video via USB in firmware - I can just plug an AV cable into the video out port, capture that data somehow, transmit, recieve and display it. Also the idea of housing the whole thing on the hotshoe is pretty smart too. edit 3: well now thinking about this again all I'd really need is an OLED display that can accept an external video signal then, and a longish (10'?) cable to run up to the camera and plug in. Hooray for over-thinking it! Any suggestions on where I can find something like that? Cannister fucked around with this message at 18:56 on Apr 14, 2011 |
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Apr 14, 2011 18:23
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Has anyone worked with solder paste? I'm about to try soldering a board with many surface mount components, and a friend convinced me to use the toaster oven route with solder paste. I'm looking for recommendations on what solder paste to get or who to order from. Is this any good? http://www.zeph.com/zephpaste.htm
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Apr 15, 2011 02:55
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I figured this maybe the best place to post this... Are there any Controls Engineers or EE's that have PLC experience? I'm a E-tech by trade and just started to play around with Schneider (telemecanique) stuff (gently caress AB). I'm looking to convert some old analog motor controls we have into PLC logic and nice HMI's. Not to poo poo up this thread but I have some pretty "basic" questions on how to compare two analog signals from two Pot's into one reference to a motor drive via a PLC. We just run the two Pots now into a few 347 op amps and such, but going digital maybe a problem for me. Halp.
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Apr 15, 2011 02:59
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Krenzo posted:Has anyone worked with solder paste? I'm about to try soldering a board with many surface mount components, and a friend convinced me to use the toaster oven route with solder paste. I'm looking for recommendations on what solder paste to get or who to order from. Is this any good? http://www.zeph.com/zephpaste.htm I've done this before. I can't really recommend it because the boards change color (some sort of chemical change it what is basically a dielectric) and it's not all that fast. I spent a couple days with the toaster oven and a thermometer matching the oven temperature to the recommended reflow curve, and the result still had to be cleaned up manually. You probably want a solder paste with a lower temperature and a slow reflow curve. That stuff might be fine but the lack of datasheets is off-putting.
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Apr 15, 2011 03:05
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Been tinkering around with a glorified drum trigger/signal gater. It takes an input signal, either a touch mic or an audio signal, being sent to a window comparator. When triggered this charges a capacitor which is run through an adjustable comparator giving a "hold" circuit. With some inverters and switches I can choose how the signal is gated and held. The logic highs and lows are run through an electronic switch setting several channels of audio on or off. If you use the incoming signal to gate itself it works as a crude noise gate. The basic circuit is working pretty good so far, considering my limited knowledge. 
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Apr 15, 2011 05:14
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Krenzo posted:Has anyone worked with solder paste? I'm about to try soldering a board with many surface mount components, and a friend convinced me to use the toaster oven route with solder paste. I'm looking for recommendations on what solder paste to get or who to order from. Is this any good? http://www.zeph.com/zephpaste.htm
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Apr 15, 2011 07:59
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Krenzo posted:Has anyone worked with solder paste? I'm about to try soldering a board with many surface mount components, and a friend convinced me to use the toaster oven route with solder paste. I'm looking for recommendations on what solder paste to get or who to order from. Is this any good? http://www.zeph.com/zephpaste.htm The only situations where using solder paste makes sense is either when you are assembling many copies of the same board and have a solder stencil, or when you are soldering very difficult packages (basically anything with multiple unexposed pads). Otherwise a soldering iron is always faster and easier (since you will likely have to touch up most connections with an iron anyways).
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Apr 15, 2011 12:41
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Doing down to 0603 packages isn't too hard as long as you have a good light source, tweezers and some way of magnifying the work.
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Apr 15, 2011 16:24
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ohgodohgodohgod Is this a good starting Arduino board? http://www.coolcomponents.co.uk/catalog/product_info.php?cPath=50_75&products_id=596
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Apr 15, 2011 17:05
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Seems as good as any.
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Apr 15, 2011 17:07
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ANIME AKBAR posted:...or when you are soldering very difficult packages (basically anything with multiple unexposed pads). Otherwise a soldering iron is always faster and easier (since you will likely have to touch up most connections with an iron anyways). I'm using 402 components and QFN chips for a board that will be operating in the 3-4 ghz range. I could solder the QFN chips, but it sounded like paste would be a lot easier to deal with.
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Apr 15, 2011 18:16
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If it turns out the toaster oven doesn't work well for reflow, you might be able to use the oven as a ghetto hotplate to preheat the board and then solder with a hot air pencil.
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Apr 15, 2011 18:22
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Fat Turkey posted:ohgodohgodohgod Is this a good starting Arduino board? I've never used any of them myself, but if I was still starting out with microcontrollers I'd be all over the Arduino boards that are designed to socket into breadboards.
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Apr 15, 2011 19:08
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I brought a small lcd. It has a FPC connector, whats the best way to to get these connections to a breadboard? I've seen video on youtube and they have loads of wires everywhere but what kind of connection is needed between the FPC and wires? The datasheet of the LCD I got is http://www.farnell.com/datasheets/341001.pdf
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Apr 15, 2011 19:44
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It might be a bit tricky mating a 0.012" cable to a 0.100" breadboard. Combined with the prohibitive cost of FPC, it may be worthwhile to seek a different connector.
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Apr 15, 2011 20:57
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Ok, I just received my components in the mail, and they came with a notice saying I had to bake them for 24 hours at 125C if I'm going to be doing solder reflow: http://www.siliconfareast.com/baketables.htm Does that still count if I choose instead to solder them with an iron and not use a toaster oven?
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Apr 15, 2011 21:01
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Krenzo posted:Ok, I just received my components in the mail, and they came with a notice saying I had to bake them for 24 hours at 125C if I'm going to be doing solder reflow: http://www.siliconfareast.com/baketables.htm It certainly wouldn't hurt, but its probably not necessary. That said, I've never seen a part fracture due to moisture absorption, so I don't know. Some companies have always been obsessive about sending out all their parts in sealed bags with silica gel packets, others just in a bit of antistatic foam. But, yeah, you hopefully shouldn't be heating the package material enough for this to be an issue if you are hand soldering, and you know what you're doing. The only exception would be for high power chips that have a large internal heatsink, which might transfer a lot more heat to the package when soldering the ground pins (assuming those are the ones attached to the heatsink).
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Apr 16, 2011 00:03
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sixide posted:It might be a bit tricky mating a 0.012" cable to a 0.100" breadboard. Combined with the prohibitive cost of FPC, it may be worthwhile to seek a different connector. How do people usually prototype when using lcd displays? I though all LCDs use FPC connectors?
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Apr 16, 2011 00:43
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Beats me. http://www.tplabs.info/ These things exist, but I haven't seen one for 0.012" pitch and 67+ pins. edit: Whoops, should have looked again. http://www.proto-advantage.com/store/product_info.php?products_id=3400028
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Apr 16, 2011 01:28
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Krenzo posted:Ok, I just received my components in the mail, and they came with a notice saying I had to bake them for 24 hours at 125C if I'm going to be doing solder reflow: http://www.siliconfareast.com/baketables.htm Don't worry about it. The concern is that in a standard reflow oven, the temperature will change fairly rapidly. Because the entire component is heated, if there is significant moisture that has condensed in the package it will vaporize and could crack the package. Since you're only heating one pin at a time, I wouldn't bother with it. Even if you were reflowing, I probably wouldn't worry. It's only when you're doing high volume manufacturing and concerned about yields that you might care.
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Apr 16, 2011 01:51
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The only time I worry about moisture content is for large (and I'm talking LARGE) MLCC capacitors. Even 1.5mm tall 1210's I've done without baking or preheating, but that's about the limit. I'm not sure what's going to be the best way to do some 0402's... Please tell me you are talking English 0402, not metric. (1.0mm x 0.5mm, not 0.4mm x 0.2mm). This is the method I use for stuff this small: http://www.youtube.com/watch?v=66GV4OuShzI If you don't have solder wire that fine (10 mil) you can essentially carry solder to the joint on an iron tip if your tips are in very good shape and you use plenty of flux on the part. I think it'll be very hard without some kind of magnification though. My buddy has reworked 0201's (0.6mm x 0.3mm) at work under a microscope, and it's not a lot of fun. QFN's are doable without paste but not without hot air. http://store.curiousinventor.com/guides/Surface_Mount_Soldering/QFN Rescue Toaster fucked around with this message at 03:15 on Apr 16, 2011 |
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Apr 16, 2011 03:13
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Thanks for the reassurances. I'm going to give a go with the soldering iron first. I have a good tip and magnification and have done other small components before just not this small.
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Apr 16, 2011 05:49
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Fat Turkey posted:ohgodohgodohgod Is this a good starting Arduino board? I have that one and it's pretty OK. It's designed to interface with the arduino expansion cards but with a couple of wires connecting it to a breadboard is no problem.
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Apr 16, 2011 17:46
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Whoop, I'm in the coilgun club now. I get sucky range and speed though, even with 5x 10mF capacitors charged to 35 volts. The problem is that the wire I'm using for everything is too high-gauge, especially the coil. I had a roll of 28 gauge magnet wire that I used which is definitely too high as the resistance of the coil is 1.6 ohms. When I get a chance to buy better wire I'll make an upgraded coil and try testing it again.
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Apr 17, 2011 03:34
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BattleMaster posted:I've never used any of them myself, but if I was still starting out with microcontrollers I'd be all over the Arduino boards that are designed to socket into breadboards. I second this, my Arduino Duemilanove has been gathering dust since I got a "Boarduino"which plugs straight into a breadboard.
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Apr 17, 2011 04:34
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Ok, got a basic project idea, a little unorthodox. I want to make a sort-of homemade security monitor. I'm thinking a microcontroller with the following inputs: 1. Temperature 2. Motion detector (movement in past 24 hours) 3. Light level Now there are two ways to get that data to me: 1. Ethernet connection to my router, have the device somehow send e-mail every X hours or when something significantly changes 2. Have a RS-232 connection from the microcontroller to a modem As far as the modem goes, I'd just make a long-distance call to my apartment, and have the microcontroller initialize the modem on boot (send a command that specifies 9600 baud, parity, answer on the first ring) and just wait for me to phone home to it. After initializing, the microcontroller would just send text data to the RS-232 port every 10 seconds or so. Would either of these approaches work?
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Apr 17, 2011 15:09
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Three-Phase posted:
When one of my friends was doing information collection from remote weather stations, he used a GSM modem to transmit text messages to a central server. You could have the system text you every hour with "ok" and immediately any time there was an event. Just another thought, I don't know how the costs on that would work out since you need a sim card and cell service. It might be cheaper than adding a second phone line though.
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Apr 17, 2011 15:50
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Also there are cell modems that use standard command sets, I found one in the trash which supports voice calls, GSM modem and SMS features, the latter two over the serial port. E: A Wavecom WMOD 2, I'm actually planning to do something similar only monitoring network and power at home. longview fucked around with this message at 17:17 on Apr 17, 2011 |
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Apr 17, 2011 17:12
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Three-Phase posted:Ok, got a basic project idea, a little unorthodox. Why not RS-232 to your computer and write a Python (or something) script that talks with it and sends you e-mail? You need a third-party library for talking to serial devices but the script would be super-easy and an RS-232 connection to a PC is also super-easy. Or is the system going to be too far from a PC for that to be viable?
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Apr 17, 2011 17:19
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