I've needed a rangefinder for some surveying stuff (not hugely accurate type of work, just me being lazy and not walking), so I needed something with compass and tilt sensing built in. Plus I wanted one that would save the data. Of course there are few of those, and pricey, so I bought an opti-logic 400LH off ebay in the hopes I could determine how it worked. I thought I would have a reasonable chance at it since the same company makes a module with RS-232 output. After numerous trial and errors, I think I have worked it out. There is an 11 pin connector that ties the main board in the the pulse generator and sensor sub-boards. Plenty of action on lots of those pins. I can't work out what most of the are, some are pulse start and maybe even sensor received. I did find one that seemed to be a clock, though it has two positive pulses in groups, and fires a total of 28 pulses. The data sheet for the rs232 module version says the raw output is 0-4095 counts, so 12 bits. I am guessing here that the last 12 pairs are the data clocked out. Pin for data is the 4th one, pin for clock is the 6th one, with numbers starting closest to battery The reason it is clocked out is there is a sub-assembly that has an ST processor and a MEMSIC accelerometer to provide the tilt compensation. Data is sent out even if this board is unplugged, but if you swith to mode 2 (horizontal corrected mode) the instrument always says zero (it waits for a response and eventually times out). To do something I chose to "ignore" the first 4 clocks, then sample the data on the falling edge of the first clock pulse out of each two (the data line seemed to always change state on the second clock edge). For the shown segment, the value is 000001100011 MSB first (99). [attachment=1] I plotted the decimal result versus feet displayed on the lcd of the 400LH and the graph is attached. The correlation is not totally perfect because I used each distance measurement, because in mode 1 (and 2, I did not test 3 or 4) on the 400LH, there appear to be a total of 8 laser firings which are then averaged to get the final value. [attachment=0] Hope this is useful to some.
By turning off the transmitter current rapidly I want to create a large EM field in anything conductive that is near the loop. I can measure the secondary field and get an idea what is going on geologically. (Yes, it is somewhat interpretive and kind of like magic...). The faster I can turn off the transmitter current, the better the field.
Thanks for the suggestions and encouragement, it always helps to discuss these things. At first I don't plan on limiting the current through any sophisticated means, except probably with my lab supply and/or a series resistor. I know analog methods of limiting current might not be ideal for power saving, but they should be good for noise and ease of use. I am not too sure that I want to introduce high frequency switching noise in the supply, although with proper filtering that might not be an issue (but to start with I am going easy). The coil resistance will depend on the coil size and wire used. This could be anywhere from 10 meters a side (square usually) to 1000 meters. Obviously wire gauge is important, (and so is weight to haul it around). Just roughly the resistance will be on the order of 40 to 400 ohms. This is why I would like to eventually limit current.
Hi all, I'm playing around with time-domain electromagnetics as would be used in geology (TDEM) and of course wondering if I can build my own transmitter. [attachment=0] Basically need to have what is essentially (or rather ideally) a square wave of really low frequency that can be turned off very rapidly (on the order of 20-30 microseconds though up to 100 would work). By turn off, I mean shutting off the current to zero, not the field. It would be good to be able to reverse the direction of current as shown in the diagram. Does it make sense to use an H-bridge for this type of application? The first prototype would be somewhat low amperage+voltage (maybe 12 or 24 V with 2 amps), but its not unheard of to use hundreds of volts and several amps (eventually, but I don't need the first prototype to be so dangerous). Eventually I would like to be able to regulate the current and voltage, but one thing at a time. thanks
Thanks Bertho, I will likely tie into the same battery for simplicity, so galvanic isolation is somewhat more difficult that way. Thanks for pointing out the current requirements for optos, that is a great point, and it might be too much for the micro or cmos logic on the other side. I don't think speed is an issue, fastest signal is probably on the order of 400 - 500 Hz. I think i will try with the level shifters and see what happens.
Hi All, I have a micro (psoc) that is running at 3.3 or 5 V (have not decided yet, but prob 5 due to improved analog specs). Of course I have to interface to the real world -- in this case an old-school magnetometer that run on 13.5V CMOS (well, on 12 D batteries till they droop too low so range 14.4 down to something like 10 I i think). I need a logic interface to this device -- there are 7 lines that I need to monitor with the micro, and another one I need to assert. It uses inverse logic (so asserts low). Would the recommendation here be optocouplers or not worry about the isolation and use something like the CD40109B-Q1 which can take overvoltage to 18 in both directions and seems to go high-low and low-high. galvanic isolation might be nice for keeping the noise out of the instrument though. thanks in advance
I recently got a stereo scope (used leica for sub $200) and love it, makes SMD work nearly trivial. Only thing it does not have a light source, so I need to come up with a good solution to that, on the cheap of course...
If you are looking for fast op amps, they do exist. Analog Devices makes one with a 1GHz -3db bandwidth -- of course you have limit the output swing to 0.1 Vpp, but even at 2 Vpp out you can get 200 MHz. I am sure there are others.
I use laen's dorkbotPDX PCB batch service. maybe not the cheapest around but the boards are really good quality. I think you might be international, so shipping might be extra added cost.
Great! thanks for working on this. I was just going to ask what you were planning on using for the programmer, but it seems you will be doing it with the miniprog. I seem to remember reading somewhere the SWD function was strange on these chips in that it needed the full jtag interface to get it going. Am I mistaken? What are the chances the bus blaster or bus pirate can program these? cheers.
