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by grahamed
Mon Nov 24, 2014 7:14 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: 5v laser module controlled by a GPIO
Replies: 9
Views: 5712

Re: 5v laser module controlled by a GPIO

Hi

I'd be interested to hear more of the action of R2.
by grahamed
Mon Nov 24, 2014 10:33 am
Forum: Automation, sensing and robotics
Topic: Installing relays to control hard-wired circuits
Replies: 6
Views: 2133

Re: Installing relays to control hard-wired circuits

Hi A few partial answers, but more musing.....and a hope for further ideas.... AFAIK in UK at least there are no commercial add-ons as you describe for the domestic situation. You can produce such a situation but only by replacing, or building with appropriate, circuits. Such things only happen in t...
by grahamed
Wed Nov 19, 2014 5:52 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: [Solved] Interfacing an atmega328p chip
Replies: 3
Views: 891

Re: Interfacing an atmega328p chip

Hi It is not necessary to be so accurate - leave out the 12R - and in fact the exactness of the theory will not carry over into practice for any number of reasons. Personally I would go with increasing both the remaining resistors x10 (1k2 and 2k2). Why ask the Arduino to provide 14mA when 1.4mA is ...
by grahamed
Wed Nov 19, 2014 3:47 pm
Forum: Automation, sensing and robotics
Topic: Wireless hall effect sensor
Replies: 9
Views: 2999

Re: Wireless hall effect sensor

Hi I probably can't do sums anymore but I make it nearer 30rps. Anyway so you stick a magnet somewhere and your Hall effect sensor gives a pulse of maybe 1ms every 30ms. The sensor datasheet shows it switching 150mA in load through an npn.. Make the load the 433MHz transmitter and it will produce a ...
by grahamed
Sat Nov 15, 2014 5:41 pm
Forum: Automation, sensing and robotics
Topic: capacitor value to add delay in circuit
Replies: 12
Views: 5209

Re: capacitor value to add delay in circuit

Hi Well, if LTSpice says it will work then I guess it will work, except the sim stopped at the LEDs and can't include the relays anyway. I seem to remember a previous thread about solenoids that didn't want to pull in, does rise time of current affect pull-in behaviour? As for ngspice - who knows. M...
by grahamed
Sat Nov 15, 2014 11:47 am
Forum: Automation, sensing and robotics
Topic: Wireless hall effect sensor
Replies: 9
Views: 2999

Re: Wireless hall effect sensor

Hi You say you don't know electronics and that's OK but if you want people to help you need to provide a bit more detail. What hall-effect sensor? What are you trying to detect? How long will the sensor be on, and off, and how often? What distance between tx and rx? Joan alludes that an Arduino is o...
by grahamed
Sat Nov 15, 2014 11:22 am
Forum: Automation, sensing and robotics
Topic: capacitor value to add delay in circuit
Replies: 12
Views: 5209

Re: capacitor value to add delay in circuit

Hi You will notice I gave myself a bit of wiggle-room there..... But then this is a high-gain Darlington and IC is very low so maybe.... I tried it using LTSpice. It seems that a 10k/47u will give almost a 1s delay, but the rise-time is slow so maybe the relay will chatter and this is not a rigorous...
by grahamed
Fri Nov 14, 2014 8:31 pm
Forum: Automation, sensing and robotics
Topic: capacitor value to add delay in circuit
Replies: 12
Views: 5209

Re: capacitor value to add delay in circuit

Hi I too am a loss as to why add a delay in the hardware but hey, maybe the OP has his reasons. There are so many issues here....but it is not easy to see how a turn-on delay could be implemented using a single C or even a single RC despite that RC product has the dimension seconds. NTE2018/ULN2803 ...
by grahamed
Fri Nov 14, 2014 5:27 pm
Forum: Automation, sensing and robotics
Topic: Protect raspberry pi against voltage spikes
Replies: 9
Views: 3895

Re: Protect raspberry pi against voltage spikes

Hi As the man says sounds like an EMI (electromagnetic interference) problem. Basically as the switch closes electrons accelerate, this causes radiation, and some part of your circuit is acting as a receiver. Two ways to a cure . 1) prevent the radiation. Generally a simple switching action should n...
by grahamed
Fri Nov 07, 2014 5:50 pm
Forum: Automation, sensing and robotics
Topic: How do I? Turn on 12v IR LED from PI?
Replies: 12
Views: 7407

Re: How do I? Turn on 12v IR LED from PI?

Hi Ah yes. the point of this thread..... three problems - I wouldn't use a Darlington, but if you have one to hand...... Only one resistor needed (between GPIO and base) but to calculate its value we need base current, for that we need current gain and collector current neither of which are known, a...
by grahamed
Fri Nov 07, 2014 3:39 pm
Forum: Automation, sensing and robotics
Topic: How do I? Turn on 12v IR LED from PI?
Replies: 12
Views: 7407

Re: How do I? Turn on 12v IR LED from PI?

Hi To be honest BSS170 is not useful for switching anything more than the smallest current irrespective of VGS. RDS=5ohm means its rated 350mA will drop 1V75 and will over-heat it in short order. If I wanted high-side switching I'd go for Mahjongg's circuit with R2 removed and T2 substituted by a pF...
by grahamed
Fri Nov 07, 2014 3:17 pm
Forum: Automation, sensing and robotics
Topic: 24VDC to 5VDC
Replies: 5
Views: 3433

Re: 24VDC to 5VDC

Hi Step up or down makes little real difference. I power all my stuff from 19V5 laptop supplies - step-down to 5V for the Pi (at the Pi) and 12V for relays/motors and such. Is the industrial LED single function - just one on-off device? Have you already a 5V supply? If so I'd look at a step-up and c...
by grahamed
Wed Nov 05, 2014 9:33 pm
Forum: Automation, sensing and robotics
Topic: How do I? Turn on 12v IR LED from PI?
Replies: 12
Views: 7407

Re: How do I? Turn on 12v IR LED from PI?

Hi again

What am I thinking of - Imax cannot be calculated like that - complete nonsense.

Still the datasheet does say continuous max current will be less than the quoted 350mA. Looking at the graphs it seems that the device might act like a 50-100mA constant current source at VGS=3V3. YMMV.
by grahamed
Wed Nov 05, 2014 8:23 pm
Forum: Automation, sensing and robotics
Topic: How do I? Turn on 12v IR LED from PI?
Replies: 12
Views: 7407

Re: How do I? Turn on 12v IR LED from PI?

Hi all I see the LED array is specified for 12V so no resistor is needed. Current is not specified as far as I can see.. NTJS3157N vs. BS170 vs. TIP120 driving the LED directly. NTJS3157N RDS = 0.055ohm @ VGS=2.5V, ICmax =4A BS170 RDS = 5ohm @ VGS = 10V, ICmax=0.5A pulsed or 70mA continuous (due to ...
by grahamed
Tue Nov 04, 2014 4:01 pm
Forum: Automation, sensing and robotics
Topic: How do I? Turn on 12v IR LED from PI?
Replies: 12
Views: 7407

Re: How do I? Turn on 12v IR LED from PI?

Oh I am impressed.

The thing just timed out and all my comments vanished.

So I'll leave it at -

if you choose the FET carefully, like NTJS3157N if don't mind surface mount, you only need a single FET (and a IMHO a gate stopper resistor).
by grahamed
Mon Nov 03, 2014 10:13 pm
Forum: Automation, sensing and robotics
Topic: How do I? Turn on 12v IR LED from PI?
Replies: 12
Views: 7407

Re: How do I? Turn on 12v IR LED from PI?

Hi Use a single FET which can take the required current (1), stand the required voltage (2) and turn on with the available drive voltage (3). These are - (1) depends on your LED array (2) 12V (3) Pi GPIO voltage 3V3 There are many such "logic level" FETs. The datasheet gives the acceptable values in...
by grahamed
Wed Oct 22, 2014 10:54 pm
Forum: Automation, sensing and robotics
Topic: Driving 5v solenoid with transistor
Replies: 9
Views: 3180

Re: Driving 5v solenoid with transistor

Hi

As you say, but hFE still applies, at least in part, whereas a single BJT......not at all.....
by grahamed
Tue Oct 21, 2014 6:18 pm
Forum: Automation, sensing and robotics
Topic: Driving 5v solenoid with transistor
Replies: 9
Views: 3180

Re: Driving 5v solenoid with transistor

HI and a much higher value base resistor.... A Darlington does well to drop less than 1V2 so coil voltage even lower. Interesting though, generally hFE does not apply to saturated transistors, in the case of a Darlington - which can never saturate, I guess hFE might apply. OK 12V supply and Darlington
by grahamed
Tue Oct 21, 2014 5:02 pm
Forum: Automation, sensing and robotics
Topic: Driving 5v solenoid with transistor
Replies: 9
Views: 3180

Re: Driving 5v solenoid with transistor

Hi Really if it pulls in reasonably smartly with 5V directly applied then it ought to pull in via the transistor. If the 5V remains as 5V and the transistor is on (i.e. the collector is pulled down to almost zero) why wouldn't it? You seem to be losing about 0V5 in the transistor - is this really en...
by grahamed
Tue Oct 21, 2014 1:15 pm
Forum: Automation, sensing and robotics
Topic: Driving 5v solenoid with transistor
Replies: 9
Views: 3180

Re: Driving 5v solenoid with transistor

Hi I take it the coil will not pull in with 5V applied directly to it.... From the datasheet (as far as I can understand it) and Burngate's analysis you probably have the 30R version. Solenoids don't generally have a fixed voltage specification as the required voltage depends on the required force. ...
by grahamed
Tue Oct 14, 2014 11:20 am
Forum: Automation, sensing and robotics
Topic: Making LEDs Light Up to Bass
Replies: 6
Views: 4201

Re: Making LEDs Light Up to Bass

Hi The strips are usually 12V, but will run from 9V.... 3 LEDs from a strip - 9V battery.jpg The strips consist of multiple modules, wired in parallel. Each module comprises 3 LEDs and a resistor, wired in series. You can just see the resistor where the strip lies adjacent to the corner of the batte...
by grahamed
Mon Oct 13, 2014 4:47 pm
Forum: Automation, sensing and robotics
Topic: Making LEDs Light Up to Bass
Replies: 6
Views: 4201

Re: Making LEDs Light Up to Bass

Hi

12V LED strips will run on 12V, from a 12V battery, or a general purpose 12V supply, or a PSU specified as suitable to drive LEDs -at least mine will.
by grahamed
Sat Oct 11, 2014 4:24 pm
Forum: Automation, sensing and robotics
Topic: MOSFET switching recommendation, please. (solved)
Replies: 13
Views: 3958

Re: SOLVED: MOSFET switching recommendation, please.

Hi

OK I did not understand that the temperature sensor is I2C......

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