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Forum Index : Microcontroller and PC projects : Maximite Power up problem
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Grogster Admin Group  Joined: 31/12/2012 Location: New ZealandPosts: 9307 |
Certainly a 5W zener could be used, but a 7812 regulator as a pre-regulator would most likey be cheaper then the 5W zener would be, and would do the same thing. 
Should not a zener be connected ACROSS the supply(with a load resistor), rather then in series with it? Smoke makes things work. When the smoke gets out, it stops! |
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| robert.rozee Guru  Joined: 31/12/2012 Location: New ZealandPosts: 2350 |
given a 24v supply, and a desire to 'lose' 12 volts, just a zener in series (reverse biased) will give a fixed voltage drop (across the zener) for loads over 5mA or so. if one has a suitable zener sitting in the junk box (12 to 15 volts), this can be a quick and simple solution. as an aside, a similar trick can be used to convert an old (pre-ATX) computer power supply into a workshop 12v supply. PC power supplies generally regulate on the 5v line. locate where the 5v is monitored, lift the connection and insert a 7.5v zener between that point and the 12v output. also add a 470 ohm resistor from the bottom end of the zener to the 0v rail to provide the necessary 10mA bias to the zener. this will give you a 12.5v or thereabouts PSU able to deliver a few amps, already built into a convenient metal box. |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9307 |
Re: Zener - Ahhh - I see.  I don't have the need to use zener's that much, and the last time I remember reading about them, it was reverse-bias with load resistor across the supply - but as I say - I don't use them that much, so not really my field.
Re: ATX PSU - I have seen a lot of those videos on YouTube. Generally, they don't seem to do anything more then just grounding or pulling high the PG(Power Good) line to make the PSU fire up. Again - not my field, and I have never built one of those, but I don't think any of them ever needed you to crack open the PSU and add bits. Still, whatever works!  Smoke makes things work. When the smoke gets out, it stops! |
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jebz Regular Member  Joined: 13/06/2011 Location: AustraliaPosts: 79 |
For 24v power in I'd use a newer switch mode regulator like this 78SR5 - http://www.ledsales.com.au/catalog/index.php?main_page=produ ct_info&cPath=142_146&products_id=840 |
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| paceman Guru Joined: 07/10/2011 Location: AustraliaPosts: 1329 |
They look like good options, even if a bit pricier. Looking at the data sheet though you'd only start getting the higher efficiencies above about 200mA. I guess at that load there shouldn't be a heat problem though. |
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panky Guru Joined: 02/10/2012 Location: AustraliaPosts: 1101 |
Hi Guys, My two penneth worth - I have been running a CG Color Maximite 24/7 for over 10 days now as the controller for my Caravan Battery Voltage Monitor. I have it configured for 4 analogue inputs and with power coming from the caravan battery/solar controller/240VAC charger. Input is noisy and with pulses from the two input chargers (solar and 240VAC). Voltage varies from 14.4V down to less than 12.4V at night. I feed the battery/charger input voltage through an LM317T variable voltage reg set to 9V to feed into the CG CMM. The system is solid as a rock. Bottom line - even in an enclosed area (front boot of the van) on days with temp up to 40C the CG CMM runs at normal temp to touch (ie. feels the same as the surrounding aluminium shell of the van boot). Temp ain't an issue unless there is some other problem. My two bobs worth ( yeah, I know, things just keep getting more expensive - EXCEPT CG's great little CG CMM) on this temp issue! The PIC chip has an inbuilt power dissapation which should NOT be an issue (as Geoff says). If you try to sink too much current with multiple digital inputs, you are going to run into problems unless you ensure your load resistors are adequate to limit the sink current. Great job CG, mine is a ripper and I will be ordering another as soon as V2 specs are finalised. It MUST have a better VGA connector that is mechanically more robust. Other than that, I don't have any real additional requirements other than perhaps a breakout of the COM pins prior to the RS232 converter so I can interface to a Bluetooth module. I definately want the sea of holes - mine is a wire wrap development area. Again, my two bobs worth - I have been playing with electronic circuits for over 45 years and I have never had a problem with static if you use common sense. ie. Either go the whole hog with anti static mats and wrist pads etc. or just ground one hand before you touch anything else on the device you are playing with ( and by the way, NOT stroking the cat on your lap would be a GOOD idea!!!). It's not rocket science guys, just common sense. Cheers, Doug. ... almost all of the Maximites, the MicromMites, the MM Extremes, the ArmMites, the PicoMite and loving it! |
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| Grogster Admin Group Joined: 31/12/2012 Location: New ZealandPosts: 9307 |
Well, that is encouraging, considering that I have jyst purchased a CMM from CG.
On the touching of circuits, yes i have to agree with you - so long as you touch an earthed metal object before touching the MM(or other), I have never EVER had a problem with blowing a static sensitive device IN CIRCUIT. Out of circuit, is another matter. Smoke makes things work. When the smoke gets out, it stops! |
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